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Search for "photoredox" in Full Text gives 133 result(s) in Beilstein Journal of Organic Chemistry.
Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis
- Shahboz Yakubov and
- Joshua P. Barham
Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183
- . One exciting development in C–F bond formation is the use of small-molecule photosensitizers, allowing the reactions i) to proceed under mild conditions, ii) to be user-friendly, iii) to be cost-effective and iv) to be more amenable to scalability than typical photoredox-catalyzed methods. In this
- reactions proceed under photoredox catalysis (PRC), involving Dexter electron transfer. Such photoredox reactions begin with the excitation of the photocatalyst (PC) by visible light, followed by a single-electron transfer (SET) between the excited photocatalyst and another molecule (quencher, Scheme 2A
Graphical Abstract
Figure 1: Fluorine-containing drugs.
Figure 2: Fluorinated agrochemicals.
Scheme 1: Selectivity of fluorination reactions.
Scheme 2: Different mechanisms of photocatalytic activation. Sub = substrate.
Figure 3: Jablonski diagram showing visible-light-induced energy transfer pathways: a) absorption, b) IC, c) ...
Figure 4: Schematic illustration of TTET.
Figure 5: Organic triplet PSCats.
Figure 6: Additional organic triplet PSCats.
Figure 7: A) Further organic triplet PSCats and B) transition metal triplet PSCats.
Figure 8: Different fluorination reagents grouped by generation.
Scheme 3: Synthesis of Selectfluor®.
Scheme 4: General mechanism of PS TTET C(sp3)–H fluorination.
Scheme 5: Selective benzylic mono- and difluorination using 9-fluorenone and xanthone PSCats, respectively.
Scheme 6: Chen’s photosensitized monofluorination: reaction scope.
Scheme 7: Chen’s photosensitized benzylic difluorination reaction scope.
Scheme 8: Photosensitized monofluorination of ethylbenzene on a gram scale.
Scheme 9: Substrate scope of Tan’s AQN-photosensitized C(sp3)–H fluorination.
Scheme 10: AQN-photosensitized C–H fluorination reaction on a gram scale.
Scheme 11: Reaction mechanism of the AQN-assisted fluorination.
Figure 9: 3D structures of the singlet ground and triplet excited states of Selectfluor®.
Scheme 12: Associated transitions for the activation of acetophenone by violet light.
Scheme 13: Ethylbenzene C–H fluorination with various PSCats and conditions.
Scheme 14: Effect of different PSCats on the C(sp3)–H fluorination of cyclohexane (39).
Scheme 15: Reaction scope of Chen’s acetophenone-photosensitized C(sp3)–H fluorination reaction.
Figure 10: a) Site-selectivity of Chen’s acetophenone-photosensitized C–H fluorination reaction [201]. b) Site-sele...
Scheme 16: Formation of the AQN–Selectfluor® exciplex Int1.
Scheme 17: Generation of the C3 2° pentane radical and the Selectfluor® N-radical cation from the exciplex.
Scheme 18: Hydrogen atom abstraction by the Selectfluor® N-radical cation from pentane to give the C3 2° penta...
Scheme 19: Fluorine atom transfer from Selectfluor® to the C3 2° pentane radical to yield 3-fluoropentane and ...
Scheme 20: Barrierless fluorine atom transfer from Int1 to the C3 2° pentane radical to yield 3-fluoropentane,...
Scheme 21: Ketone-directed C(sp3)–H fluorination.
Scheme 22: Ketone-directed fluorination through a 5- and a 6-membered transition state, respectively.
Scheme 23: Effect of different PSCats on the photosensitized C(sp3)–H fluorination of 47.
Scheme 24: Substrate scope of benzil-photoassisted C(sp3)–H fluorinations.
Scheme 25: A) Benzil-photoassisted enone-directed C(sp3)–H fluorination. B) Classification of the reaction mod...
Scheme 26: A) Xanthone-photoassisted ketal-directed C(sp3)–H fluorination. B) Substrate scope. C) C–H fluorina...
Scheme 27: Rationale for the selective HAT at the C2 C–H bond of galactose acetonide.
Scheme 28: Photosensitized C(sp3)–H benzylic fluorination of a peptide using different PSCats.
Scheme 29: Peptide scope of 5-benzosuberenone-photoassisted C(sp3)–H fluorinations.
Scheme 30: Continuous flow PS TTET monofluorination of 72.
Scheme 31: Photosensitized C–H fluorination of N-butylphthalimide as a PSX.
Scheme 32: Substrate scope and limitations of the PSX C(sp3)–H monofluorination.
Scheme 33: Substrate crossover monofluorination experiment.
Scheme 34: PS TTET mechanism proposed by Hamashima and co-workers.
Scheme 35: Photosensitized TFM of 78 to afford α-trifluoromethylated ketone 80.
Scheme 36: Substrate scope for photosensitized styrene TFM to give α-trifluoromethylated ketones.
Scheme 37: Control reactions for photosensitized TFM of styrenes.
Scheme 38: Reaction mechanism for photosensitized TFM of styrenes to afford α-trifluoromethylated ketones.
Scheme 39: Reaction conditions for TFMs to yield the cis- and the trans-product, respectively.
Scheme 40: Substrate scope of trifluoromethylated (E)-styrenes.
Scheme 41: Strategies toward trifluoromethylated (Z)-styrenes.
Scheme 42: Substrate scope of trifluoromethylated (Z)-styrenes.
Scheme 43: Reaction mechanism for photosensitized TFM of styrenes to afford E- or Z-products.
Reactions of 3-aryl-1-(trifluoromethyl)prop-2-yn-1-iminium salts with 1,3-dienes and styrenes
- Thomas Schneider,
- Michael Keim,
- Bianca Seitz and
- Gerhard Maas
Beilstein J. Org. Chem. 2020, 16, 2064–2072, doi:10.3762/bjoc.16.173
- lithium acetylides [25]. By a photoredox-catalytic process, primary α-(trifluoromethyl)-α-(4-pyridyl)benzylamines were obtained from α-(trifluoromethyl)-benzaldoximes and 4-cyanopyridine [26]. We have recently introduced a new class of acetylenic iminium salts, namely 1-(trifluoromethyl)prop-2-yn-1
Graphical Abstract
Scheme 1: Diels–Alder reaction of propyn-1-iminium salt 1a compared with the reported [29] reaction of 4-phenyl-1...
Scheme 2: Sequential Diels–Alder/intramolecular SE(Ar) reaction of propyn-1-iminium triflates 1a,b. Condition...
Scheme 3: Diels–Alder reaction of 1a and anthracene followed by an intramolecular SE(Ar) reaction.
Figure 1: Solid-state molecular structure of 11 (ORTEP plot).
Scheme 4: Reactions of propyn-1-iminium salt 1a with styrenes.
Figure 2: Solid-state molecular structure of 12c (ORTEP plot).
Figure 3: Solid-state molecular structure of 12d (ORTEP plot). Both the R and the S enantiomer are present in...
Scheme 5: A mechanistic proposal for the reaction of alkyne 1a with styrenes.
Scheme 6: Reaction of alkyne 1a with 1,2-dihydronaphthalene.
Scheme 7: Synthesis and solid-state molecular structure (ORTEP plot) of pentafulvene 19; selected bond distan...
Scheme 8: Proposed mechanistic pathway leading to fulvene 19.
A complementary approach to conjugated N-acyliminium formation through photoredox-catalyzed intermolecular radical addition to allenamides and allencarbamates
- Olusesan K. Koleoso,
- Matthew Turner,
- Felix Plasser and
- Marc C. Kimber
Beilstein J. Org. Chem. 2020, 16, 1983–1990, doi:10.3762/bjoc.16.165
- radical addition, using photoredox catalysis, to allenamides and allencarbamates is reported. This transformation synthesizes N-acyl-N’-aryl-N,N’-allylaminals, and proceeds by a conjugated N-acyliminium intermediate that previously has principally been generated by electrophilic activation methods. The
- radical adds to the central carbon of the allene giving a conjugated N-acyliminium that undergoes nucleophilic addition by arylamines and alcohols. Keywords: allenamide; allene; intermolecular; N-acyliminium; photoredox; Introduction Allenamides (Scheme 1, 1) and their congeners have attracted
- subsequently formed radical (Scheme 3) [41]. The thought process behind this approach is based on three observations; (i) Akita and co-workers disclosure on the photoredox-catalyzed oxytrifluoromethylation of allenes 6 to give 2-trifluoromethylated allyl acetates 7 [42][43][44]; (ii) that intramolecular
Graphical Abstract
Scheme 1: Electrophilic activation of allenamides.
Scheme 2: The planned intramolecular radical addition to allenamides generating the conjugated N-acyliminium ...
Scheme 3: Photoredox Ir-catalyzed intermolecular addition of bromide 18 and aniline 16 to allenamide 15.
Scheme 4: Reaction scope (a) allenamide; (b) arylamine nucleophile; (c) alcohol nucleophile.
Scheme 5: (a) Tentative mechanism for the photoredox-catalyzed formation of the conjugated N-acyliminium inte...
When metal-catalyzed C–H functionalization meets visible-light photocatalysis
- Lucas Guillemard and
- Joanna Wencel-Delord
Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147
- previous functionalization, thus considerably reduce waste generation and a number of synthetic steps. In parallel, transformations involving photoredox catalysis promote radical reactions in the absence of radical initiators. They are conducted under particularly mild conditions while using the visible
- catalytic system is extremely appealing. In that perspective, the scope of this review aims to present innovative reactions combining C–H activation and visible-light induced photocatalysis. Keywords: C–H activation; C–H functionalization; dual catalysis; photoredox catalysis; radical chemistry
- )) [47]. Despite great advances achieved in the field of both, C–H activation and visible-light-induced photocatalysis, dual systems merging these two activation modes have remained underdeveloped until recently. In contrast, over the past decade, the design of new strategies combining photoredox
Graphical Abstract
Figure 1: Concept of dual synergistic catalysis.
Figure 2: Classification of catalytic systems involving two catalysts.
Figure 3: General mechanism for the dual nickel/photoredox catalytic system.
Figure 4: General mechanisms for C–H activation catalysis involving different reoxidation strategies.
Figure 5: Indole synthesis via dual C–H activation/photoredox catalysis.
Figure 6: Proposed mechanism for the indole synthesis via dual catalysis.
Figure 7: Oxidative Heck reaction on arenes via the dual catalysis.
Figure 8: Proposed mechanism for the Heck reaction on arenes via dual catalysis.
Figure 9: Oxidative Heck reaction on phenols via the dual catalysis.
Figure 10: Proposed mechanism for the Heck reaction on phenols via dual catalysis.
Figure 11: Carbazole synthesis via dual C–H activation/photoredox catalysis.
Figure 12: Proposed mechanism for the carbazole synthesis via dual catalysis.
Figure 13: Carbonylation of enamides via the dual C–H activation/photoredox catalysis.
Figure 14: Proposed mechanism for carbonylation of enamides via dual catalysis.
Figure 15: Annulation of benzamides via the dual C–H activation/photoredox catalysis.
Figure 16: Proposed mechanism for the annulation of benzamides via dual catalysis.
Figure 17: Synthesis of indoles via the dual C–H activation/photoredox catalysis.
Figure 18: Proposed mechanism for the indole synthesis via dual catalysis.
Figure 19: General concept of dual catalysis merging C–H activation and photoredox catalysis.
Figure 20: The first example of dual catalysis merging C–H activation and photoredox catalysis.
Figure 21: Proposed mechanism for the C–H arylation with diazonium salts via dual catalysis.
Figure 22: Dual catalysis merging C–H activation/photoredox using diaryliodonium salts.
Figure 23: Direct arylation via the dual catalytic system reported by Xu.
Figure 24: Direct arylation via dual catalytic system reported by Balaraman.
Figure 25: Direct arylation via dual catalytic system reported by Guo.
Figure 26: C(sp3)–H bond arylation via the dual Pd/photoredox catalytic system.
Figure 27: Acetanilide derivatives acylation via the dual C–H activation/photoredox catalysis.
Figure 28: Proposed mechanism for the C–H acylation with α-ketoacids via dual catalysis.
Figure 29: Acylation of azobenzenes via the dual catalysis C–H activation/photoredox.
Figure 30: C2-acylation of indoles via the dual C–H activation/photoredox catalysis.
Figure 31: Proposed mechanism for the C2-acylation of indoles with aldehydes via dual catalysis.
Figure 32: C2-acylation of indoles via the dual C–H activation/photoredox catalysis.
Figure 33: Perfluoroalkylation of arenes via the dual C–H activation/photoredox catalysis.
Figure 34: Proposed mechanism for perfluoroalkylation of arenes via dual catalysis.
Figure 35: Sulfonylation of 1-naphthylamides via the dual C–H activation/photoredox catalysis.
Figure 36: Proposed mechanism for sulfonylation of 1-naphthylamides via dual catalysis.
Figure 37: meta-C–H Alkylation of arenes via visible-light metallaphotocatalysis.
Figure 38: Alternative procedure for meta-C–H alkylation of arenes via metallaphotocatalysis.
Figure 39: Proposed mechanism for meta-C–H alkylation of arenes via metallaphotocatalysis.
Figure 40: C–H borylation of arenes via visible-light metallaphotocatalysis.
Figure 41: Proposed mechanism for C–H borylation of arenes via visible-light metallaphotocatalysis.
Figure 42: Undirected C–H aryl–aryl cross coupling via dual gold/photoredox catalysis.
Figure 43: Proposed mechanism for the undirected C–H aryl–aryl cross-coupling via dual catalysis.
Figure 44: Undirected C–H arylation of (hetero)arenes via dual manganese/photoredox catalysis.
Figure 45: Proposed mechanism for the undirected arylation of (hetero)arenes via dual catalysis.
Figure 46: Photoinduced C–H arylation of azoles via copper catalysis.
Figure 47: Photo-induced C–H chalcogenation of azoles via copper catalysis.
Figure 48: Decarboxylative C–H adamantylation of azoles via dual cobalt/photoredox catalysis.
Figure 49: Proposed mechanism for the C–H adamantylation of azoles via dual catalysis.
Figure 50: General mechanisms for the “classical” (left) and Cu-free variant (right) Sonogoshira reaction.
Figure 51: First example of a dual palladium/photoredox catalysis for Sonogashira-type couplings.
Figure 52: Arylation of terminal alkynes with diazonium salts via dual gold/photoredox catalysis.
Figure 53: Proposed mechanism for the arylation of terminal alkynes via dual catalysis.
Figure 54: C–H Alkylation of alcohols promoted by H-atom transfer (HAT).
Figure 55: Proposed mechanism for the C–H alkylation of alcohols promoted by HAT.
Figure 56: C(sp3)–H arylation of latent nucleophiles promoted by H-atom transfer.
Figure 57: Proposed mechanism for the C(sp3)–H arylation of latent nucleophiles promoted by HAT.
Figure 58: Direct α-arylation of alcohols promoted by H-atom transfer.
Figure 59: Proposed mechanism for the direct α-arylation of alcohols promoted by HAT.
Figure 60: C–H arylation of amines via dual Ni/photoredox catalysis.
Figure 61: Proposed mechanism for the C–H arylation of amines via dual Ni/photoredox catalysis.
Figure 62: C–H functionalization of nucleophiles via excited ketone/nickel dual catalysis.
Figure 63: Proposed mechanism for the C–H functionalization enabled by excited ketones.
Figure 64: Selective sp3–sp3 cross-coupling promoted by H-atom transfer.
Figure 65: Proposed mechanism for the selective sp3–sp3 cross-coupling promoted by HAT.
Figure 66: Direct C(sp3)–H acylation of amines via dual Ni/photoredox catalysis.
Figure 67: Proposed mechanism for the C–H acylation of amines via dual Ni/photoredox catalysis.
Figure 68: C–H hydroalkylation of internal alkynes via dual Ni/photoredox catalysis.
Figure 69: Proposed mechanism for the C–H hydroalkylation of internal alkynes.
Figure 70: Alternative procedure for the C–H hydroalkylation of ynones, ynoates, and ynamides.
Figure 71: Allylic C(sp3)–H activation via dual Ni/photoredox catalysis.
Figure 72: Proposed mechanism for the allylic C(sp3)–H activation via dual Ni/photoredox catalysis.
Figure 73: Asymmetric allylation of aldehydes via dual Cr/photoredox catalysis.
Figure 74: Proposed mechanism for the asymmetric allylation of aldehydes via dual catalysis.
Figure 75: Aldehyde C–H functionalization promoted by H-atom transfer.
Figure 76: Proposed mechanism for the C–H functionalization of aldehydes promoted by HAT.
Figure 77: Direct C–H arylation of strong aliphatic bonds promoted by HAT.
Figure 78: Proposed mechanism for the C–H arylation of strong aliphatic bonds promoted by HAT.
Figure 79: Direct C–H trifluoromethylation of strong aliphatic bonds promoted by HAT.
Figure 80: Proposed mechanism for the C–H trifluoromethylation of strong aliphatic bonds.
Photoredox-catalyzed silyldifluoromethylation of silyl enol ethers
- Vyacheslav I. Supranovich,
- Vitalij V. Levin and
- Alexander D. Dilman
Beilstein J. Org. Chem. 2020, 16, 1550–1553, doi:10.3762/bjoc.16.126
- -electron oxidation thereby supporting a photoredox cycle [22][23][24]. The silyl enol ether 2a derived from acetophenone was selected as a model substrate and the reaction with silane 1 (1.5 equiv) was evaluated (Scheme 2). The reactions were performed in dichloromethane, and reaction mixtures were
- employed in photoredox reactions to scavenge acidic byproducts [28][29], could not be employed. Silane 1 is easily destroyed by bases (even by the amide group [30]) followed by the rapid addition of difluorocarbene to silyl enol ethers [19][20]. Disappointingly, we were unable to isolate ketone 3a using
- borohydride, and the decreased reactivity of this ketone allowed its isolation. A proposed mechanism for the photoredox fluoroalkylation reaction is shown in Scheme 3. The photoexcited catalyst converts silane 1 into difluoromethylsilyl-based radical. The efficiency of [AuCl(μ-dppm)]2 compared to other
Graphical Abstract
Scheme 1: Reactions of (bromodifluoromethyl)trimethylsilane (1).
Scheme 2: Optimization studies. Yield determined by 19F NMR spectroscopy using an internal standard.
Figure 1: Reaction of silyl enol ethers. Yields refer to isolated yields. aReaction time 24 h; b1.0 equiv of ...
Scheme 3: Proposed mechanism of the fluoroalkylation reaction.
Heterogeneous photocatalysis in flow chemical reactors
- Christopher G. Thomson,
- Ai-Lan Lee and
- Filipe Vilela
Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125
- some interesting reactor designs that could be implemented to enhance organic synthesis. Keywords: air purification; flow chemistry; heterogeneous photoredox catalysis; organic synthesis; reactor design; water purification; Review 1 Introduction 1.1 Scope of the review This review aims to be of
- discussion of the advantages and disadvantages to guide the reader in selecting the reactor best suited to their system. Following this, in Section 4, we review the recent applications of HPCats in flow reactors for synthetic organic chemistry through photoredox catalysis (PRC, Section 4.1) and energy
- visible light through single-electron transfer processes, now referred to as visible light photoredox catalysis (PRC). A similar query on the Web of Science for the term “Photoredox” clearly shows the surge in PRC research following those reports, from 2010 onwards (Figure 1A). However, what is
Graphical Abstract
Figure 1: A) Bar chart of the publications per year for the topics “Photocatalysis” (49,662 instances) and “P...
Figure 2: A) Professor Giacomo Ciamician and Dr. Paolo Silber on their roof laboratory at the University of B...
Scheme 1: PRC trifluoromethylation of N-methylpyrrole (1) using hazardous gaseous CF3I safely in a flow react...
Figure 3: A) Unit cells of the three most common crystal structures of TiO2: rutile, brookite, and anatase. R...
Figure 4: Illustration of the key semiconductor photocatalysis events: 1) A photon with a frequency exceeding...
Figure 5: Photocatalytic splitting of water by oxygen vacancies on a TiO2(110) surface. Reprinted with permis...
Figure 6: Proposed adsorption modes of A) benzene, B) chlorobenzene, C) toluene, D) phenol, E) anisole, and F...
Figure 7: Structures of the sulfonate-containing organic dyes RB5 (3) and MX-5B (4) and the adsorption isothe...
Figure 8: Idealised triclinic unit cell of a g-C3N4 type polymer, displaying possible hopping transport scena...
Figure 9: Idealised structure of a perfect g-C3N4 sheet. The central unit highlighted in red represents one t...
Figure 10: Timeline of the key processes of charge transport following the photoexcitation of g-C3N4, leading ...
Scheme 2: Photocatalytic bifunctionalisation of heteroarenes using mpg-C3N4, with the selected examples 5 and ...
Figure 11: A) Structure of four linear conjugated polymer photocatalysts for hydrogen evolution, displaying th...
Figure 12: Graphical representation of the common methods used to immobilise molecular photocatalysts (PC) ont...
Figure 13: Wireless light emitter-supported TiO2 (TiO2@WLE) HPCat spheres powered by resonant inductive coupli...
Figure 14: Graphical representation of zinc–perylene diimide (Zn-PDI) supramolecular assembly photocatalysis v...
Scheme 3: Upconversion of NIR photons to the UV frequency by NaYF4:Yb,Tm nanocrystals sequentially coated wit...
Figure 15: Types of reactors employed in heterogeneous photocatalysis in flow. A) Fixed bed reactors and the s...
Figure 16: Electrochemical potential of common semiconductor, transition metal, and organic dye-based photocat...
Scheme 4: Possible mechanisms of an immobilised molecular photoredox catalyst by oxidative or reductive quenc...
Scheme 5: Scheme of the CMB-C3N4 photocatalytic decarboxylative fluorination of aryloxyacetic acids, with the...
Scheme 6: Scheme of the g-C3N4 photocatalytic desilylative coupling reaction in flow and proposed mechanism [208].
Scheme 7: Proposed mechanism of the radical cyclisation of unsaturated alkyl 2-bromo-1,3-dicarbonyl compounds...
Scheme 8: N-alkylation of benzylamine and schematic of the TiO2-coated microfluidic device [213].
Scheme 9: Proposed mechanism of the Pt@TiO2 photocatalytic deaminitive cyclisation of ʟ-lysine (23) to ʟ-pipe...
Scheme 10: A) Proposed mechanism for the photocatalytic oxidation of phenylboronic acid (24). B) Photos and SE...
Scheme 11: Proposed mechanism for the DA-CMP3 photocatalytic aza-Henry reaction performed in a continuous flow...
Scheme 12: Proposed mechanism for the formation of the cyclic product 32 by TiO2-NC HPCats in a slurry flow re...
Scheme 13: Reaction scheme for the photocatalytic synthesis of homo and hetero disulfides in flow and scope of...
Scheme 14: Reaction scheme for the MoOx/TiO2 HPCat oxidation of cyclohexane (34) to benzene. The graph shows t...
Scheme 15: Proposed mechanism of the TiO2 HPC heteroarene C–H functionalisation via aryl radicals generated fr...
Scheme 16: Scheme of the oxidative coupling of benzylamines with the HOTT-HATN HPCat and selected examples of ...
Scheme 17: Photocatalysis oxidation of benzyl alcohol (40) to benzaldehyde (41) in a microflow reactor coated ...
Figure 17: Mechanisms of Dexter and Forster energy transfer.
Scheme 18: Continuous flow process for the isomerisation of alkenes with an ionic liquid-immobilised photocata...
Scheme 19: Singlet oxygen synthetic step in the total synthesis of canataxpropellane [265].
Scheme 20: Scheme and proposed mechanism of the singlet oxygen photosensitisation by CMP_X HPCats, with the st...
Scheme 21: Structures of CMP HPCat materials applied by Vilela and co-workers for the singlet oxygen photosens...
Scheme 22: Polyvinylchloride resin-supported TDCPP photosensitisers applied for singlet oxygen photosensitisat...
Scheme 23: Structure of the ionically immobilised TPP photosensitiser on amberlyst-15 ion exchange resins (TPP...
Scheme 24: Photosensitised singlet oxygen oxidation of citronellol (46) in scCO2, with automatic phase separat...
Scheme 25: Schematic of PS-Est-BDP-Cl2 being applied for singlet oxygen photosensitisation in flow. A) Pseudo-...
Scheme 26: Reaction scheme of the singlet oxygen oxidation of furoic acid (54) using a 3D-printed microfluidic...
Figure 18: A) Photocatalytic bactericidal mechanism by ROS oxidative cleavage of membrane lipids (R = H, amino...
Figure 19: A) Suggested mechanisms for the aqueous pollutant degradation by TiO2 in a slurry flow reactor [284-287]. B)...
Figure 20: Schematic of the flow system used for the degradation of aqueous oxytetracycline (56) solutions [215]. M...
Scheme 27: Degradation of a salicylic acid (57) solution by a coupled solar photoelectro-Fenton (SPEF) process...
Figure 21: A) Schematic flow diagram using the TiO2-coated NETmix microfluidic device for an efficient mass tr...
Photocatalyzed syntheses of phenanthrenes and their aza-analogues. A review
- Alessandra Del Tito,
- Havall Othman Abdulla,
- Davide Ravelli,
- Stefano Protti and
- Maurizio Fagnoni
Beilstein J. Org. Chem. 2020, 16, 1476–1488, doi:10.3762/bjoc.16.123
- is a quite unexplored field, a notable exception being the seminal work published in 1984 by Cano-Yelo and Deronzier, where the authors reported one of the first applications of the Ru(bpy)32+ complex in photoredox catalysis (Scheme 1). This contribution described a photo-Pschorr cyclization
- biaryls 5.1a–d in up to excellent yields at room temperature by using α-bromoesters as radical precursors and [fac-Ir(ppy)3] as the photoredox catalyst [49]. A similar photocatalyzed tandem insertion/cyclization approach based on isocyanides and amino acid/peptide-derived Katritzky salts as precursors of
- - [55][56] phenanthridines was investigated. On the other hand, Umemoto’s reagent 7.2 was widely employed to introduce a trifluoromethyl group. In one instance, the visible-light irradiation of isocyanides 7.1 in the presence of excess 7.2 (4 equiv) and the Ru(bpy)32+ photoredox catalyst afforded the
Graphical Abstract
Figure 1: Bioactive phenanthridine and phenanthridinium derivatives.
Scheme 1: Synthesis of phenanthrenes by a photo-Pschorr reaction.
Scheme 2: Synthesis of phenanthrenes by a benzannulation reaction.
Scheme 3: Photocatalytic cyclization of α-bromochalcones for the synthesis of phenanthrenes.
Figure 2: Carbon-centered and nitrogen-centered radicals used for the synthesis of phenanthridines.
Scheme 4: General scheme describing the synthesis of phenanthridines from isocyanides via imidoyl radicals.
Scheme 5: Synthesis of substituted phenanthridines involving the intermediacy of electrophilic radicals.
Scheme 6: Photocatalyzed synthesis of 6-β-ketoalkyl phenanthridines.
Scheme 7: Synthesis of 6-substituted phenanthridines through the addition of trifluoromethyl (path a), phenyl...
Scheme 8: Synthesis of 6-(trifluoromethyl)-7,8-dihydrobenzo[k]phenanthridine.
Scheme 9: Phenanthridine syntheses by using photogenerated radicals formed through a C–H bond homolytic cleav...
Scheme 10: Trifluoroacetimidoyl chlorides as starting substrates for the synthesis of 6-(trifluoromethyl)phena...
Scheme 11: Synthesis of phenanthridines via aryl–aryl-bond formation.
Scheme 12: Oxidative conversion of N-biarylglycine esters to phenanthridine-6-carboxylates.
Scheme 13: Photocatalytic synthesis of benzo[f]quinolines from 2-heteroaryl-substituted anilines and heteroary...
Scheme 14: Synthesis of noravicine (14.2a) and nornitidine (14.2b) alkaloids.
Scheme 15: Gram-scale synthesis of the alkaloid trisphaeridine (15.3).
Scheme 16: Synthesis of phenanthridines starting from vinyl azides.
Scheme 17: Synthesis of pyrido[4,3,2-gh]phenanthridines 17.5a–d through the radical trifluoromethylthiolation ...
Scheme 18: The direct oxidative C–H amidation involving amidyl radicals for the synthesis of phenanthridones.
An overview on disulfide-catalyzed and -cocatalyzed photoreactions
- Yeersen Patehebieke
Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118
- . Under photoirradiation, organic disulfides can be easily cleaved into free thiyl radicals (RS•) and can reversibly add to unsaturated multiple bonds to catalyze a variety of functionalization reactions under mild conditions. In photoredox catalysis reactions, an excellent electron transfer ability and
- variety of reactions, renders them a class of green, economic, mild, and chemoselective radical catalyst. Apart from this, they are also excellent HAT catalysts in photoredox catalysis systems [2][3]. In various types of organic photochemistry reactions, such as cyclizations, anti-Markovnikov additions
- method is also applicable for the synthesis of a wide variety of cyclopentane derivatives [12]. In 2017, Huang and co-workers reported a [4 + 2] cycloaddition reaction promoted by blue LED light, using aromatic olefins as the precursor, an acridinium photoredox catalyst (Mes–Acr–Ph+BF4−), and disulfide
Graphical Abstract
Scheme 1: [3 + 2] cyclization catalyzed by diaryl disulfide.
Scheme 2: [3 + 2] cycloaddition catalyzed by disulfide.
Scheme 3: Disulfide-bridged peptide-catalyzed enantioselective cycloaddition.
Scheme 4: Disulfide-catalyzed [3 + 2] methylenecyclopentane annulations.
Scheme 5: Disulfide as a HAT cocatalyst in the [4 + 2] cycloaddition reaction.
Scheme 6: Proposed mechanism of the [4 + 2] cycloaddition reaction using disulfide as a HAT cocatalyst.
Scheme 7: Disulfide-catalyzed ring expansion of vinyl spiro epoxides.
Scheme 8: Disulfide-catalyzed aerobic oxidation of diarylacetylene.
Scheme 9: Disulfide-catalyzed aerobic photooxidative cleavage of olefins.
Scheme 10: Disulfide-catalyzed aerobic oxidation of 1,3-dicarbonyl compounds.
Scheme 11: Proposed mechanism of the disulfide-catalyzed aerobic oxidation of 1,3-dicarbonyl compounds.
Scheme 12: Disulfide-catalyzed oxidation of allyl alcohols.
Scheme 13: Disulfide-catalyzed diboration of alkynes.
Scheme 14: Dehalogenative radical cyclization catalyzed by disulfide.
Scheme 15: Hydrodifluoroacetamidation of alkenes catalyzed by disulfide.
Scheme 16: Plausible mechanism of the hydrodifluoroacetamidation of alkenes catalyzed by disulfide.
Scheme 17: Disulfide-cocatalyzed anti-Markovnikov olefin hydration reactions.
Scheme 18: Disulfide-catalyzed decarboxylation of carboxylic acids.
Scheme 19: Proposed mechanism of the disulfide-catalyzed decarboxylation of carboxylic acids.
Scheme 20: Disulfide-catalyzed decarboxylation of carboxylic acids.
Scheme 21: Disulfide-catalyzed conversion of maleate esters to fumarates and 5H-furanones.
Scheme 22: Disulfide-catalyzed isomerization of difluorotriethylsilylethylene.
Scheme 23: Disulfide-catalyzed isomerization of allyl alcohols to carbonyl compounds.
Scheme 24: Proposed mechanism for the disulfide-catalyzed isomerization of allyl alcohols to carbonyl compound...
Scheme 25: Diphenyl disulfide-catalyzed enantioselective synthesis of ophirin B.
Scheme 26: Disulfide-catalyzed isomerization in the total synthesis of (+)-hitachimycin.
Scheme 27: Disulfide-catalyzed isomerization in the synthesis of (−)-gloeosporone.
Distinctive reactivity of N-benzylidene-[1,1'-biphenyl]-2-amines under photoredox conditions
- Shrikant D. Tambe,
- Kwan Hong Min,
- Naeem Iqbal and
- Eun Jin Cho
Beilstein J. Org. Chem. 2020, 16, 1335–1342, doi:10.3762/bjoc.16.114
- but also as electron donors in the photoredox cycle, and the results are reported herein. We began with the reaction of simple N-benzylideneaniline. However, this substrate did not furnish the desired products under several different photocatalysis conditions, including those reported by Rueping. We
- partner and an electron donor in the photoredox cycle (Scheme 1c). It is likely that the presence of the additional phenyl group in the substrate stabilizes the α-amino radical intermediate and modulates its reactivity [46][47]. In addition to the cross-coupled 1,2-diamines, we envisioned the generation
Graphical Abstract
Scheme 1: Photocatalytic transformations of imines.
Scheme 2: Substrate scope for the radical cross-couplings. Reaction conditions: 1 (0.3 mmol), under argon atm...
Scheme 3: Substrate scope for the homocoupling. Reaction conditions: 1 (0.3 mmol), under argon atmosphere, is...
Scheme 4: Reduction of the imine 1a to the amine 4a.
Scheme 5: Proposed mechanism.
Photocatalytic trifluoromethoxylation of arenes and heteroarenes in continuous-flow
- Alexander V. Nyuchev,
- Ting Wan,
- Borja Cendón,
- Carlo Sambiagio,
- Job J. C. Struijs,
- Michelle Ho,
- Moisés Gulías,
- Ying Wang and
- Timothy Noël
Beilstein J. Org. Chem. 2020, 16, 1305–1312, doi:10.3762/bjoc.16.111
- residence time up to 16 times in comparison to the batch procedure, while achieving similar or higher yields. In addition, the use of inorganic bases was demonstrated to increase the reaction yield under batch conditions. Keywords: C–H functionalization; continuous-flow; organic synthesis; photoredox
- , partially due to the general interest of the community into C–H functionalization methodologies [18][19], and partially thanks to the synthetic possibilities enabled by photoredox catalysis, a field widely explored in recent years [20][21][22]. In 2018, Ngai [23][24] and Togni [25] reported simple
- photoredox protocols for the radical trifluoromethoxylation of unfunctionalized (hetero)arenes by using specifically designed CF3O radical-releasing agents (Scheme 1B). Following our long-standing interest in the development of continuous-flow approaches for C–H functionalization [18][26] and photochemical
Graphical Abstract
Scheme 1: A) Properties and B) synthesis of CF3O-bearing arenes; C) trifluoromethoxylation using the “second”...
Scheme 2: Optimization of residence time. 19F NMR yields are reported.
Scheme 3: Scope of photoredox trifluoromethoxylation in continuous-flow. In case of different products, the m...
Figure 1: Effect of KH2PO4 – other substrates. a Conditions as for entry 15 (Table 2), 1 h residence time; b conditi...
Oxime radicals: generation, properties and application in organic synthesis
- Igor B. Krylov,
- Stanislav A. Paveliev,
- Alexander S. Budnikov and
- Alexander O. Terent’ev
Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107
Graphical Abstract
Figure 1: Imine-N-oxyl radicals (IV) discussed in the present review and other classes of N-oxyl radicals (I–...
Figure 2: The products of decomposition of iminoxyl radicals generated from oximes by oxidation with Ag2O.
Scheme 1: Generation of oxime radicals and study of the kinetics of their decay by photolysis of the solution...
Scheme 2: Synthesis of di-tert-butyliminoxyl radical and its decomposition products.
Scheme 3: The proposed reaction pathway of the decomposition of di-tert-butyliminoxyl radical (experimentally...
Scheme 4: Monomolecular decomposition of the tert-butyl(triethylmethyl)oxime radical.
Scheme 5: The synthesis and stability of the most stable dialkyl oxime radicals – di-tert-butyliminoxyl and d...
Scheme 6: The formation of iminoxyl radicals from β-diketones under the action of NO2.
Scheme 7: Synthesis of the diacetyliminoxyl radical.
Scheme 8: Examples of long-living oxime radicals with electron-withdrawing groups and the conditions for thei...
Figure 3: The electronic structure iminoxyl radicals and their geometry compared to the corresponding oximes.
Figure 4: Bond dissociation enthalpies (kcal/mol) of oximes and N,N-disubstituted hydroxylamines calculated o...
Scheme 9: Examples demonstrating the low reactivity of the di-tert-butyliminoxyl radical towards the substrat...
Scheme 10: The reactions of di-tert-butyliminoxyl radical with unsaturated hydrocarbons involving hydrogen ato...
Scheme 11: Possible mechanisms of reaction of di-tert-butyliminoxyl radical with alkenes.
Scheme 12: Products of the reaction between di-tert-butyliminoxyl radical and phenol derivatives.
Scheme 13: The reaction of di-tert-butyliminoxyl radical with amines.
Scheme 14: Reaction of di-tert-butyliminoxyl radicals with organolithium reagents.
Scheme 15: Cross-dehydrogenative C–O coupling of 1,3-dicarbonyl compounds with oximes under the action of mang...
Scheme 16: Cross-dehydrogenative C–O coupling of 1,3-dicarbonyl compounds with oximes under the action of Cu(BF...
Scheme 17: Oxidative C–O coupling of benzylmalononitrile (47) with 3-(hydroxyimino)pentane-2,4-dione (19).
Scheme 18: The proposed mechanism of the oxidative coupling of benzylmalononitrile (47) with diacetyl oxime (19...
Scheme 19: Oxidative C–O coupling of pyrazolones with oximes under the action of Fe(ClO4)3.
Scheme 20: The reaction of diacetyliminoxyl radical with pyrazolones.
Scheme 21: Oxidative C–O coupling of oximes with acetonitrile, ketones, and esters.
Scheme 22: Intramolecular cyclizations of oxime radicals to form substituted isoxazolines or cyclic nitrones.
Scheme 23: TEMPO-mediated oxidative cyclization of oximes with C–H bond cleavage.
Scheme 24: Proposed reaction mechanism of oxidative cyclization of oximes with C–H bond cleavage.
Scheme 25: Selectfluor/Bu4NI-mediated C–H oxidative cyclization of oximes.
Scheme 26: Oxidative cyclization of N-benzyl amidoximes to 1,2,4-oxadiazoles.
Scheme 27: The formation of quinazolinone 73a from 5-phenyl-4,5-dihydro-1,2,4-oxadiazole 74 under air.
Scheme 28: DDQ-mediated oxidative cyclization of thiohydroximic acids.
Scheme 29: Plausible mechanism of the oxidative cyclization of thiohydroximic acids.
Scheme 30: Silver-mediated oxidative cyclization of α-halogenated ketoximes and 1,3-dicarbonyl compounds.
Scheme 31: Possible pathway of one-pot oxidative cyclization of α-halogenated ketoximes and 1,3-dicarbonyl com...
Scheme 32: T(p-F)PPT-catalyzed oxidative cyclization of oximes with the formation of 1,2,4-oxadiazolines.
Scheme 33: Intramolecular cyclization of iminoxyl radicals involving multiple C=C and N=N bonds.
Scheme 34: Oxidative cyclization of β,γ- and γ,δ-unsaturated oximes employing the DEAD or TEMPO/DEAD system wi...
Scheme 35: Cobalt-catalyzed aerobic oxidative cyclization of β,γ-unsaturated oximes.
Scheme 36: Manganese-catalyzed aerobic oxidative cyclization of β,γ-unsaturated oximes.
Scheme 37: Visible light photocatalytic oxidative cyclization of β,γ-unsaturated oximes.
Scheme 38: TBAI/TBHP-mediated radical cascade cyclization of the β,γ-unsaturated oximes.
Scheme 39: TBAI/TBHP-mediated radical cascade cyclization of vinyl isocyanides with β,γ-unsaturated oximes.
Scheme 40: tert-Butylnitrite-mediated oxidative cyclization of unsaturated oximes with the introduction of an ...
Scheme 41: Transformation of unsaturated oxime to oxyiminomethylisoxazoline via the confirmed dimeric nitroso ...
Scheme 42: tert-Butylnitrite-mediated oxidative cyclization of unsaturated oximes with the introduction of a n...
Scheme 43: Synthesis of cyano-substituted oxazolines from unsaturated oximes using the TBN/[RuCl2(p-cymene)]2 ...
Scheme 44: Synthesis of trifluoromethylthiolated isoxazolines from unsaturated oximes.
Scheme 45: Copper-сatalyzed oxidative cyclization of β,γ-unsaturated oximes with the introduction of an azido ...
Scheme 46: TBHP-mediated oxidative cascade cyclization of β,γ-unsaturated oximes and unsaturated N-arylamides.
Scheme 47: Copper-сatalyzed oxidative cyclization of unsaturated oximes with the introduction of an amino grou...
Scheme 48: TEMPO-mediated oxidative cyclization of unsaturated oximes followed by elimination.
Scheme 49: Oxidative cyclization of β,γ-unsaturated oximes with the introduction of a trifluoromethyl group.
Scheme 50: Oxidative cyclization of unsaturated oximes with the introduction of a nitrile group.
Scheme 51: Oxidative cyclization of β,γ-unsaturated oximes to isoxazolines with the introduction of a nitrile ...
Scheme 52: Oxidative cyclization of β,γ-unsaturated oximes to isoxazolines with the introduction of a sulfonyl...
Scheme 53: Oxidative cyclization of β,γ- and γ,δ-unsaturated oximes to isoxazolines with the introduction of a...
Scheme 54: Oxidative cyclization of β,γ-unsaturated oximes to isoxazolines with the introduction of a thiocyan...
Scheme 55: PhI(OAc)2-mediated oxidative cyclization of oximes with C–S and C–Se bond formation.
Scheme 56: PhI(OAc)2-mediated oxidative cyclization of unsaturated oximes accompanied by alkoxylation.
Scheme 57: PhI(OAc)2-mediated cyclization of unsaturated oximes to methylisoxazolines.
Scheme 58: Oxidative cyclization-alkynylation of unsaturated oximes.
Scheme 59: TEMPO-mediated oxidative cyclization of C-glycoside ketoximes to C-glycosylmethylisoxazoles.
Scheme 60: Silver-сatalyzed oxidative cyclization of β,γ-unsaturated oximes with formation of fluoroalkyl isox...
Scheme 61: Oxidative cyclization of β,γ-unsaturated oximes with the formation of haloalkyl isoxazolines.
Scheme 62: Cyclization of β,γ-unsaturated oximes into haloalkyl isoxazolines under the action of the halogenat...
Scheme 63: Synthesis of haloalkyl isoxazoles and cyclic nitrones via oxidative cyclization and 1,2-halogen shi...
Scheme 64: Electrochemical oxidative cyclization of diaryl oximes.
Scheme 65: Copper-сatalyzed cyclization and dioxygenation oximes containing a triple C≡C bond.
Scheme 66: Photoredox-catalyzed sulfonylation of β,γ-unsaturated oximes by sulfonyl hydrazides.
Scheme 67: Oxidative cyclization of β,γ-unsaturated oximes with introduction of sulfonate group.
Scheme 68: Ultrasound-promoted oxidative cyclization of β,γ-unsaturated oximes.
Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis
- Stephanie G. E. Amos,
- Marion Garreau,
- Luca Buzzetti and
- Jerome Waser
Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103
- Stephanie G. E. Amos Marion Garreau Luca Buzzetti Jerome Waser Laboratory of Catalysis and Organic Synthesis, Ecole Polytechnique Fédérale de Lausanne, EPFL, SB ISIC LCSO, BCH 4306 1015 Lausanne, Switzerland 10.3762/bjoc.16.103 Abstract Organic dyes have emerged as a reliable class of photoredox
- -, nitrogen-, oxygen-, and sulfur-centered radicals, open-shell charged species, and sensitized organic compounds. Keywords: organic dyes; photocatalysis; photoredox catalysis; radicals; reactive intermediates; Review Introduction In the last decade, synthetic organic chemistry has experienced the
- each of these steps, the role of A or D is assumed by a redox-active agent, either the substrate, a sacrificial electron donor/acceptor, or a reactive intermediate. This approach, usually named photoredox catalysis, has known a remarkable growth in the last decade and has given access to both neutral
Graphical Abstract
Figure 1: Selected examples of organic dyes. Mes-Acr+: 9-mesityl-10-methylacridinium, DCA: 9,10-dicyanoanthra...
Scheme 1: Activation modes in photocatalysis.
Scheme 2: Main strategies for the formation of C(sp3) radicals used in organophotocatalysis.
Scheme 3: Illustrative example for the photocatalytic oxidative generation of radicals from carboxylic acids:...
Scheme 4: Illustrative example for the photocatalytic reductive generation of C(sp3) radicals from redoxactiv...
Figure 2: Common substrates for the photocatalytic oxidative generation of C(sp3) radicals.
Scheme 5: Illustrative example for the photocatalytic oxidative generation of radicals from dihydropyridines ...
Scheme 6: Illustrative example for the photocatalytic oxidative generation of C(sp3) radicals from trifluorob...
Scheme 7: Illustrative example for the photocatalytic reductive generation of C(sp3) radicals from benzylic h...
Scheme 8: Illustrative example for the photocatalytic generation of C(sp3) radicals via direct HAT: the cross...
Scheme 9: Illustrative example for the photocatalytic generation of C(sp3) radicals via indirect HAT: the deu...
Scheme 10: Selected precursors for the generation of aryl radicals using organophotocatalysis.
Scheme 11: Illustrative example for the photocatalytic reductive generation of aryl radicals from aryl diazoni...
Scheme 12: Illustrative examples for the photocatalytic reductive generation of aryl radicals from haloarenes:...
Scheme 13: Illustrative example for the photocatalytic reductive generation of aryl radicals from aryl halides...
Scheme 14: Illustrative example for the photocatalytic reductive generation of aryl radicals from arylsulfonyl...
Scheme 15: Illustrative example for the reductive photocatalytic generation of aryl radicals from triaryl sulf...
Scheme 16: Main strategies towards acyl radicals used in organophotocatalysis.
Scheme 17: Illustrative example for the decarboxylative photocatalytic generation of acyl radicals from α-keto...
Scheme 18: Illustrative example for the oxidative photocatalytic generation of acyl radicals from acyl silanes...
Scheme 19: Illustrative example for the oxidative photocatalytic generation of carbamoyl radicals from 4-carba...
Scheme 20: Illustrative example of the photocatalytic HAT approach for the generation of acyl radicals from al...
Scheme 21: General reactivity of a) radical cations; b) radical anions; c) the main strategies towards aryl an...
Scheme 22: Illustrative example for the oxidative photocatalytic generation of alkene radical cations from alk...
Scheme 23: Illustrative example for the reductive photocatalytic generation of an alkene radical anion from al...
Figure 3: Structure of C–X radical anions and their neutral derivatives.
Scheme 24: Illustrative example for the photocatalytic reduction of imines and the generation of an α-amino C(...
Scheme 25: Illustrative example for the oxidative photocatalytic generation of aryl radical cations from arene...
Scheme 26: NCR classifications and generation.
Scheme 27: Illustrative example for the photocatalytic reductive generation of iminyl radicals from O-aryl oxi...
Scheme 28: Illustrative example for the photocatalytic oxidative generation of iminyl radicals from α-N-oxy ac...
Scheme 29: Illustrative example for the photocatalytic oxidative generation of iminyl radicals via an N–H bond...
Scheme 30: Illustrative example for the photocatalytic oxidative generation of amidyl radicals from Weinreb am...
Scheme 31: Illustrative example for the photocatalytic reductive generation of amidyl radicals from hydroxylam...
Scheme 32: Illustrative example for the photocatalytic reductive generation of amidyl radicals from N-aminopyr...
Scheme 33: Illustrative example for the photocatalytic oxidative generation of amidyl radicals from α-amido-ox...
Scheme 34: Illustrative example for the photocatalytic oxidative generation of aminium radicals: the N-aryltet...
Scheme 35: Illustrative example for the photocatalytic oxidative generation of nitrogen-centered radical catio...
Scheme 36: Illustrative example for the photocatalytic oxidative generation of nitrogen-centered radical catio...
Scheme 37: Illustrative example for the photocatalytic oxidative generation of hydrazonyl radical from hydrazo...
Scheme 38: Generation of O-radicals.
Scheme 39: Illustrative examples for the photocatalytic generation of O-radicals from N-alkoxypyridinium salts...
Scheme 40: Illustrative examples for the photocatalytic generation of O-radicals from alkyl hydroperoxides: th...
Scheme 41: Illustrative example for the oxidative photocatalytic generation of thiyl radicals from thiols: the...
Scheme 42: Main strategies and reagents for the generation of sulfonyl radicals used in organophotocatalysis.
Scheme 43: Illustrative example for the reductive photocatalytic generation of sulfonyl radicals from arylsulf...
Scheme 44: Illustrative example of a Cl atom abstraction strategy for the photocatalytic generation of sulfamo...
Scheme 45: Illustrative example for the oxidative photocatalytic generation of sulfonyl radicals from sulfinic...
Scheme 46: Illustrative example for the photocatalytic generation of electronically excited triplet states: th...
Scheme 47: Illustrative example for the photocatalytic generation of electronically excited triplet states: th...
Accelerating fragment-based library generation by coupling high-performance photoreactors with benchtop analysis
- Quentin Lefebvre,
- Christophe Salomé and
- Thomas C. Fessard
Beilstein J. Org. Chem. 2020, 16, 982–988, doi:10.3762/bjoc.16.87
- Quentin Lefebvre Christophe Salome Thomas C. Fessard SpiroChem AG, Rosental area, WRO-1047-3, Mattenstrasse 24, 4058 Basel, Switzerland 10.3762/bjoc.16.87 Abstract Herein we report a workflow coupling photoredox-nickel dual-catalyzed N-arylation reactions to benchtop analysis for the efficient
- thus be rapidly accessed, identifying privileged or challenging scaffolds and paving the way for further exploration. Keywords: benchtop analytics; fragment-based library; heterocyclic sp2–sp3 fragments; N-arylation; photoredox-nickel dual catalysis; Introduction Heterocyclic sp2–sp3 fragments are
- initiated a high-throughput program of fragment-based library generation and after shortcomings using more classical cross-coupling conditions, we turned our attention to the photoredox-nickel dual-catalysis strategy recently reported by MacMillan and Buchwald [10]. The reported conditions use lower
Graphical Abstract
Scheme 1: One-day workflow for fragment-based library generation. QC: Quality control. MPLC: Medium-pressure ...
Figure 1: Top: high-power blue LED photoreactors. Bottom, from left to right: photoreactor OFF, ON, and ON th...
Figure 2: TLC–MS equipment: analysis of 5 reactions in 5 minutes.
Figure 3: Pre-QC validation by 60 MHz benchtop NMR.
Scheme 2: Scope of the fragment-based library generation: BCP-amines and azetidines. See Supporting Information File 1 for experimental de...
Scheme 3: Scope of the fragment-based library generation: pyrrolidines, piperidines and morpholines. See Supporting Information File 1 for...
Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches
- Rodrigo Costa e Silva,
- Luely Oliveira da Silva,
- Aloisio de Andrade Bartolomeu,
- Timothy John Brocksom and
- Kleber Thiago de Oliveira
Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83
- renewal of porphyrin applications in photocatalysis. Finally, the reaction scale in which the methodologies were developed are highlighted since this is an important parameter in the authors’ opinion. Keywords: energy transfer; photocatalysis; photooxygenation; photoredox; porphyrins; Introduction In
- photoredox and energy transfer photocatalyzed reactions. The idea of this review is also to cover representative chemical transformations and recent applications in both batch and continuous-flow conditions, and emphasizing as much as possible, the scale in which the reactions were described. It is important
- to clarify that other relevant reviews reporting applications of porphyrins in different perspectives can be found in the literature [19][20][21]. In addition, we emphasize that this review is organized into two topics. The first topic highlights the reactions that employ porphyrins as photoredox
Graphical Abstract
Figure 1: Chemical structures of the porphyrinoids and their absorption spectra: in bold are highlighted the ...
Figure 2: Photophysical and photochemical processes (Por = porphyrin). Adapted from [12,18].
Figure 3: Main dual photocatalysts and their oxidative/reductive excited state potentials, including porphyri...
Scheme 1: Photoredox alkylation of aldehydes with diazo acetates using porphyrins and a Ru complex. aUsing a ...
Scheme 2: Proposed mechanism for the alkylation of aldehydes with diazo acetates in the presence of TPP.
Scheme 3: Arylation of heteroarenes with aryldiazonium salts using TPFPP as photocatalyst, and corresponding ...
Scheme 4: A) Scope with different aryldiazonium salts and enol acetates. B) Photocatalytic cycles and compari...
Scheme 5: Photoarylation of isopropenyl acetate A) Comparison between batch and continuous-flow approaches an...
Scheme 6: Dehalogenation induced by red light using thiaporphyrin (STPP).
Scheme 7: Applications of NiTPP as both photoreductant and photooxidant.
Scheme 8: Proposed mechanism for obtaining tetrahydroquinolines by reductive quenching.
Scheme 9: Selenylation and thiolation of anilines.
Scheme 10: NiTPP as photoredox catalyst in oxidative and reductive quenching, in comparison with other photoca...
Scheme 11: C–O bond cleavage of 1-phenylethanol using a cobalt porphyrin (CoTMPP) under visible light.
Scheme 12: Hydration of terminal alkynes by RhIII(TSPP) under visible light irradiation.
Scheme 13: Regioselective photocatalytic hydro-defluorination of perfluoroarenes by RhIII(TSPP).
Scheme 14: Formation of 2-methyl-2,3-dihydrobenzofuran by intramolecular hydro-functionalization of allylpheno...
Scheme 15: Photocatalytic oxidative hydroxylation of arylboronic acids using UNLPF-12 as heterogeneous photoca...
Scheme 16: Photocatalytic oxidative hydroxylation of arylboronic acids using MOF-525 as heterogeneous photocat...
Scheme 17: Preparation of the heterogeneous photocatalyst CNH.
Scheme 18: Photoinduced sulfonation of alkenes with sulfinic acid using CNH as photocatalyst.
Scheme 19: Sulfonic acid scope of the sulfonation reactions.
Scheme 20: Regioselective sulfonation reaction of arimistane.
Scheme 21: Synthesis of quinazolin-4-(3H)-ones.
Scheme 22: Selective photooxidation of aromatic benzyl alcohols to benzaldehydes using Pt/PCN-224(Zn).
Scheme 23: Photooxidation of benzaldehydes to benzoic acids using Pt or Pd porphyrins.
Scheme 24: Photocatalytic reduction of various nitroaromatics using a Ni-MOF.
Scheme 25: Photoinduced cycloadditions of CO2 with epoxides by MOF1.
Figure 4: Electronic configurations of the species of oxygen. Adapted from [66].
Scheme 26: TPP-photocatalyzed generation of 1O2 and its application in organic synthesis. Adapted from [67-69].
Scheme 27: Pericyclic reactions involving singlet oxygen and their mechanisms. Adapted from [67].
Scheme 28: First scaled up ascaridole preparation from α-terpinene.
Scheme 29: Antimalarial drug synthesis using an endoperoxidation approach.
Scheme 30: Photooxygenation of colchicine.
Scheme 31: Synthesis of (−)-pinocarvone from abundant (+)-α-pinene.
Scheme 32: Seeberger’s semi-synthesis of artemisinin.
Scheme 33: Synthesis of artemisinin using TPP and supercritical CO2.
Scheme 34: Synthesis of artemisinin using chlorophyll a.
Scheme 35: Quercitol stereoisomer preparation.
Scheme 36: Photocatalyzed preparation of naphthoquinones.
Scheme 37: Continuous endoperoxidation of conjugated dienes and subsequent rearrangements leading to oxidized ...
Scheme 38: The Opatz group total synthesis of (–)-oxycodone.
Scheme 39: Biomimetic syntheses of rhodonoids A, B, E, and F.
Scheme 40: α-Photooxygenation of chiral aldehydes.
Scheme 41: Asymmetric photooxidation of indanone β-keto esters by singlet oxygen using PTC as a chiral inducer...
Scheme 42: Asymmetric photooxidation of both β-keto esters and β-keto amides by singlet oxygen using PTC-2 as ...
Scheme 43: Bifunctional photo-organocatalyst used for the asymmetric oxidation of β-keto esters and β-keto ami...
Scheme 44: Mechanism of singlet oxygen oxidation of sulfides to sulfoxides.
Scheme 45: Controlled oxidation of sulfides to sulfoxides using protonated porphyrins as photocatalysts. aIsol...
Scheme 46: Photochemical oxidation of sulfides to sulfoxides using PdTPFPP as photocatalyst.
Scheme 47: Controlled oxidation of sulfides to sulfoxides using SnPor@PAF as a photosensitizer.
Scheme 48: Syntheses of 2D-PdPor-COF and 3D-Pd-COF.
Scheme 49: Photocatalytic oxidation of A) thioanisole to methyl phenyl sulfoxide and B) various aryl sulfides,...
Scheme 50: General mechanism for oxidation of amines to imines.
Scheme 51: Oxidation of secondary amines to imines.
Scheme 52: Oxidation of secondary amines using Pd-TPFPP as photocatalyst.
Scheme 53: Oxidative amine coupling using UNLPF-12 as heterogeneous photocatalyst.
Scheme 54: Synthesis of Por-COF-1 and Por-COF-2.
Scheme 55: Photocatalytic oxidation of amines to imines by Por-COF-2.
Scheme 56: Photocyanation of primary amines.
Scheme 57: Synthesis of ᴅ,ʟ-tert-leucine hydrochloride.
Scheme 58: Photocyanation of catharanthine and 16-O-acetylvindoline using TPP.
Scheme 59: Photochemical α-functionalization of N-aryltetrahydroisoquinolines using Pd-TPFPP as photocatalyst.
Scheme 60: Ugi-type reaction with 1,2,3,4-tetrahydroisoquinoline using molecular oxygen and TPP.
Scheme 61: Ugi-type reaction with dibenzylamines using molecular oxygen and TPP.
Scheme 62: Mannich-type reaction of tertiary amines using PdTPFPP as photocatalyst.
Scheme 63: Oxidative Mannich reaction using UNLPF-12 as heterogeneous photocatalyst.
Scheme 64: Transformation of amines to α-cyanoepoxides and the proposed mechanism.
Aldehydes as powerful initiators for photochemical transformations
- Maria A. Theodoropoulou,
- Nikolaos F. Nikitas and
- Christoforos G. Kokotos
Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76
- presented. Keywords: aldehyde; green chemistry; photochemistry; photoinitiation; sustainable chemistry; Introduction Photochemistry, and especially photoredox catalysis have altered the way that modern researchers treat radical species [1][2][3][4]. In most cases, a metal-based photocatalyst is employed
- , having multiple advantages since ligand manipulation can lead to optimized photoredox properties. Unfortunately, the use of metals can pose some critical disadvantages in an organic process. Especially since the natural abundance of various noble metals that are used as photocatalysts is limited and
- supported the energy transfer pathway. Thus, the proposed triplet sensitization mechanism of the photocatalytic ATRA reaction is depicted in Scheme 25. In 2016, Ji and co-workers developed a new photoredox cross-dehydrogenative coupling (CDC) method for the α-heteroarylation of amides (α to nitrogen, e.g
Graphical Abstract
Scheme 1: Norrish type I and II dissociations.
Scheme 2: Proposed radical pair formation after the photolysis of benzaldehyde (8).
Scheme 3: Aldehydes in the Paterno–Büchi reaction.
Scheme 4: 2,3-Diazabicyclo[2.2.1]hept-2-ene (DBH).
Scheme 5: Dissociation pathways of benzaldehyde.
Scheme 6: Reactions that lead to polarized products detectable by CIDNP.
Scheme 7: MMA (26), DEABP (27), and Michler’s ketone (28).
Scheme 8: Radical intermediates of DEABP.
Scheme 9: Photoinitiated polymerization of monomeric MMA (26) using the quinoxalines 32 and benzaldehyde (8).
Scheme 10: Acetone (4) and formaldehyde (35) as photografting initiators.
Scheme 11: Photografting by employing acetaldehyde (36) as the photoinitiator.
Scheme 12: Proposed photolysis mechanism for aliphatic ketones 44 and formaldehyde (35).
Scheme 13: Initiator 50, reductant 51, and benzaldehyde derivatives 52–54 for the polymerization of the methac...
Scheme 14: Proposed mechanism of the photomediated atom transfer radical polymerization employing the benzalde...
Scheme 15: cis/trans isomerization employing triplet states of photosensitizers.
Scheme 16: Salicylaldehyde (68) forms an internal hydrogen bond.
Scheme 17: Olefin isomerization via energy transfer from a carbonyl compound.
Scheme 18: Mechanistic pathways for the Paterno–Büchi reaction.
Scheme 19: Isomeric oxetanes formed after photochemical addition of aryl aldehydes to 2-butenes.
Scheme 20: Rotation of the C3–C4 bond of the biradical intermediate may lead to all four conformations.
Scheme 21: Photolysis products of benzaldehyde (8) in different solvents. a) In benzene or ethanol. b) In hex-...
Scheme 22: N-tert-Butylbenzamide formation proceeds via a benzoyl radical.
Scheme 23: Photochemical pinacol coupling.
Scheme 24: Photochemical ATRA catalyzed by 4-anisaldehyde (52).
Scheme 25: Proposed triplet sensitization mechanism of the ATRA reaction in the presence of 4-anisaldehyde (52...
Scheme 26: Benzaldehyde-mediated photoredox CDC reaction: compatible amides and ethers.
Scheme 27: Photoredox cross-dehydrogenative coupling (CDC) conditions and proposed reaction mechanism.
Scheme 28: Optimized conditions for the photoredox merger reaction.
Scheme 29: Proposed mechanism for the C(sp3)–H alkylation/arylation of ethers.
Scheme 30: Substrate scope for the photochemical alkylation of ethers.
Scheme 31: C(sp3)–H Functionalization of N-containing molecules.
Scheme 32: Substrate scope for the photochemical alkylation of N-containing molecules.
Scheme 33: Additional products yielded by the photochemical alkylation reaction of N-containing molecules.
Scheme 34: C(sp3)–H functionalization of thioethers.
Scheme 35: Proposed mechanism for the C(sp3)–H alkylation/arylation of N-containing molecules and thioethers.
Scheme 36: Hydroacylation using 4-cyanobenzaldehyde (53) as the photoinitiator.
Scheme 37: Selectivity for the formation of the α,α-disubstituted aldehydes.
Scheme 38: Substrate scope for the photochemical addition of aldehydes to Michael acceptors.
Scheme 39: Proposed mechanism for the hydroacylation of Michael acceptors using 4-cyanobenzaldehyde (53) as th...
Scheme 40: Catalytic arylation of aromatic aldehydes by aryl bromides in which the reaction product acts as th...
Scheme 41: Proposed mechanism for the catalytic arylation of benzaldehydes by aryl bromides in which the react...
Scheme 42: Functionalization of the chiral cyclobutanes 180.
Scheme 43: Optimized reaction conditions and proposed mechanism for the sulfonylcyanation of cyclobutenes.
Photocatalytic deaminative benzylation and alkylation of tetrahydroisoquinolines with N-alkylpyrydinium salts
- David Schönbauer,
- Carlo Sambiagio,
- Timothy Noël and
- Michael Schnürch
Beilstein J. Org. Chem. 2020, 16, 809–817, doi:10.3762/bjoc.16.74
- Dolech 2, 5612 AZ Eindhoven, The Netherlands 10.3762/bjoc.16.74 Abstract A ruthenium-catalyzed photoredox coupling of substituted N-aryltetrahydroisoquinolines (THIQs) and different bench-stable pyridinium salts was successfully developed to give fast access to 1-benzyl-THIQs. Furthermore, secondary
- (sp3) coupling; deaminative coupling; Katritzky salt; photoredox catalysis; Introduction The selective formation of new carbon–carbon bonds via direct C–H functionalization bears the potential of being a process of high efficiency [1][2][3]. Since C–H bonds are omnipresent in organic compounds it is
- ], alkynation [17][18], or allylation [19]), this method has certain drawbacks, most importantly the frequent requirement of superstoichiometric amounts of an oxidant. Hence, alternative methods were investigated and photoredox catalysis proved to be a viable option [20][21][22]. By now, several different
Graphical Abstract
Scheme 1: Examples of photocatalytic C–C bond formation by nucleophilic trapping of a reactive THIQ intermedi...
Figure 1: Kinetic profile for the benzylation of 1 to 3.
Scheme 2: Benzylation of N-phenyl-THIQ.
Scheme 3: Benzylation of substituted N-arylTHIQs.
Scheme 4: Removal of the PMP protecting group.
Scheme 5: Alkylation of N-phenyl-THIQ derivatives. Conditions: a2 mol % [Ir(dtbbpy)(ppy)2]PF6, DMA, 60 h; b2 ...
Scheme 6: Proposed mechanism.
Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0
- Bernd Strehmel,
- Christian Schmitz,
- Ceren Kütahya,
- Yulian Pang,
- Anke Drewitz and
- Heinz Mustroph
Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40
- metal ions. In this process, basically, in the presence of photoactive materials (PAs) such as photoinitiators, photosensitizers or photoredox catalysts, the photoexcitation of a photoredox system results in formation of reactive radicals. Those reactive radicals add monomer and the polymerization
Graphical Abstract
Scheme 1: Structural patterns of several symmetric cyanines relating to trimethines (I), pentamethines (II), ...
Scheme 2: 1-Substituted 2,3,3-trimethylindolium-, 2,3,3-benzo[e]indolium-, and 2,3,3-benzo[c,d]indolium salts...
Scheme 3: Substitution of the chlorine substituent at the meso-position by a stronger nucleophilic moiety B [68].
Scheme 4: Structure of alternative chain builders for synthesis of heptamethines.
Figure 1: Simplified process chart of photophysical processes occurring in NIR absorbers.
Scheme 5: Chemical structure of the electron acceptors that were from iodonium cations 88 and triazines 89.
Figure 2: Photoinduced electron transfer under different scenarios in which each example exhibits an intrinsi...
Scheme 6: Photoexcited absorber 33 results in reaction with an iodonium cation in the respective cation radic...
Scheme 7: Reaction scheme of absorbers comprising in the molecules center a five ring bridged moiety. This le...
Scheme 8: Structure of donor compounds used in a three component system.
Figure 3: Cationic photopolymerization of an epoxide (Epikote 828) initiated by excitation of the absorber 36...
Scheme 9: Different modes of photoinitiated ATRP using UV, visible and NIR light.
Scheme 10: The structure of Sens used in photo-ATRP.
Figure 4: Comparison of the GPC traces of precursor PMMA with a) chain extended PMMA and b) PMMA-b-PS. Condit...
Figure 5: Spectral changes of the solution of 48 in the presence of [Cu(L)]Br2 (L: tris(2-pyridylmethyl)amine...
Scheme 11: Photoinduced CuAAC reactions in which photochemical reactions result in formation of the Cu(I) cata...
Scheme 12: Model reaction between benzyl azide and phenyacetylene using the absorber 48 as NIR sensitizer at 7...
Figure 6: Block copolymerization of the precursors PS-N3 and Alkyne-PCL results in the block copolymer PS-b-P...
Figure 7: UV–vis–NIR absorption changes of the solution of 48 in the presence of PMDETA, phenylacetylene and ...
Scheme 13: Workflow to design and process new materials in a setup based on an intelligent DoE to develop tech...
Scheme 14: Illustration of the iDoE setting up experiments suggested and analyzed by the A.I. After defining t...
Scheme 15: Classification of the factors for the formation of polymer networks by NIR-photocuring depending on...
Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid
- Kaj M. van Vliet,
- Nicole S. van Leeuwen,
- Albert M. Brouwer and
- Bas de Bruin
Beilstein J. Org. Chem. 2020, 16, 398–408, doi:10.3762/bjoc.16.38
- traditional reactivity of this compound. Here, we investigated the possibility of applying monochloroacetic acid as a substrate for photoredox catalysis with styrene to directly produce γ-phenyl-γ-butyrolactone. Instead of using nucleophilic substitution, we cleaved the carbon chlorine bond by single-electron
- form in case of fac-[Ir(ppy)3]), which was proven by mass spectrometry and EPR spectroscopy for one of the catalysts (N,N-5,10-di(2-naphthalene)-5,10-dihydrophenazine) used in this work. The generation of HCl resulting from lactone formation could be an additional problem for organometallic photoredox
- catalysts used in this reaction. In an attempt to trap one of the radical intermediates with TEMPO, we observed a compound indicating the generation of a chloromethyl radical. Keywords: ATRA; catalysis; chloroacetic acid; lactone; photoredox; Introduction Monochloroacetic acid is an industrially important
Graphical Abstract
Figure 1: A part of the industry around monochloroacetic acid.
Scheme 1: Redox based activation of haloacetic acid.
Figure 2: Cyclic voltammogram of monochloroacetic acid and ferrocene with 0.1 M [TBA][PF6] in MeCN. The poten...
Scheme 2: Initial attempts for lactone formation by photoredox catalysis.
Scheme 3: The photoredox reaction of TEMPO with monochloroacetic acid catalyzed by fac-[Ir(ppy)3].
Figure 3: EPR spectra measured (black) and simulated (red) based on the structure of the oxidized photoredox ...
Scheme 4: Two possible acid-assisted, reductive activation pathways of monochloroacetic acid (A–H = acid).
Figure 4: Reaction mixtures after overnight irradiation of (A) 4-chloro-4-phenylbutanoic acid (3) and fac-[Ir...
Scheme 5: Substrate scope of styrene derivatives in the photoredox reaction with monochloroacetic acid. Yield...
Scheme 6: Proposed reaction mechanism.
Scheme 7: The photoredox formation of 1-(chloromethoxy)-2,2,6,6-tetramethylpiperidine.
Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations
- Rafia Siddiqui and
- Rashid Ali
Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26
- compounds, including bioactive natural and nonnatural products, but also due to its impact on the discovery of pharmaceutical candidates and the total synthesis of intricate natural products. On the other hand, more recently, the field of photoredox catalysis has become an indispensable and unparalleled
- highly desirable to the scientific community. In this review, we mainly highlight the impact on, and the utility of, photoredox catalysts in inert ortho and para C–H bond functionalizations. Although a surge of research papers, including reviews, demonstrating C–H functionalizations have been published
- in this vital area of research, to our best knowledge, this is the first review that focuses on ortho and para C–H functionalizations by photoredox catalysis to provide atom- and step-economic organic transformations. We are certain that this review will act as a promoter to highlight the application
Graphical Abstract
Figure 1: List of photoredox catalysts used for C–H bond functionalizations.
Figure 2: List of metal-based photoredox catalysts used in this review article.
Figure 3: Jablonski diagram.
Figure 4: Photoredox catalysis via reductive or oxidative pathways. D = donor, A = acceptor, S = substrate, P...
Figure 5: Schematic representation of the combination of photoredox catalysis and transition metal catalysis.
Scheme 1: Weinreb amide C–H olefination.
Figure 6: Mechanism for the formation of 21 from 19 using photoredox catalyst 11.
Scheme 2: C–H olefination of phenolic ethers.
Scheme 3: Decarboxylative acylation of acetanilides.
Figure 7: Mechanism for the formation of 30 from acetanilide derivatives.
Scheme 4: Synthesis of fluorenone derivatives by intramolecular deoxygenative acylation of biaryl carboxylic ...
Figure 8: Mechanism for the photoredox-catalyzed synthesis of fluorenone derivatives.
Scheme 5: Synthesis of benzothiazoles via aerobic C–H thiolation.
Figure 9: Plausible mechanism for the construction of benzothiazoles from benzothioamides.
Scheme 6: Synthesis of benzothiazoles via oxidant-free C–H thiolation.
Figure 10: Mechanism involved in the synthesis of benzothiazoles via oxidant-free C–H thiolation.
Scheme 7: Synthesis of indoles via C–H cyclization of anilides with alkynes.
Scheme 8: Preparation of 3-trifluoromethylcoumarins via C–H cyclization of arylpropiolate esters.
Figure 11: Mechanistic pathway for the synthesis of coumarin derivatives via C–H cyclization.
Scheme 9: Monobenzoyloxylation without chelation assistance.
Figure 12: Plausible mechanism for the formation of 71 from 70.
Scheme 10: Aryl-substituted arenes prepared by inorganic photoredox catalysis using 12a.
Figure 13: Proposed mechanism for C–H arylations in the presence of 12a and a Pd catalyst.
Scheme 11: Arylation of purines via dual photoredox catalysis.
Scheme 12: Arylation of substituted arenes with an organic photoredox catalyst.
Scheme 13: C–H trifluoromethylation.
Figure 14: Proposed mechanism for the trifluoromethylation of 88.
Scheme 14: Synthesis of benzo-3,4-coumarin derivatives.
Figure 15: Plausible mechanism for the synthesis of substituted coumarins.
Scheme 15: Oxidant-free oxidative phosphonylation.
Figure 16: Mechanism proposed for the phosphonylation reaction of 100.
Scheme 16: Nitration of anilines.
Figure 17: Plausible mechanism for the nitration of aniline derivatives via photoredox catalysis.
Scheme 17: Synthesis of carbazoles via intramolecular amination.
Figure 18: Proposed mechanism for the formation of carbazoles from biaryl derivatives.
Scheme 18: Synthesis of substituted phenols using QuCN.
Figure 19: Mechanism for the synthesis of phenol derivatives with photoredox catalyst 8.
Scheme 19: Synthesis of substituted phenols with DDQ (5).
Figure 20: Possible mechanism for the generation of phenols with the aid of photoredox catalyst 5.
Scheme 20: Aerobic bromination of arenes using an acridinium-based photocatalyst.
Scheme 21: Aerobic bromination of arenes with anthraquinone.
Figure 21: Proposed mechanism for the synthesis of monobrominated compounds.
Scheme 22: Chlorination of benzene derivatives with Mes-Acr-MeClO4 (2).
Figure 22: Mechanism for the synthesis of 131 from 132.
Scheme 23: Chlorination of arenes with 4CzIPN (5a).
Figure 23: Plausible mechanism for the oxidative photocatalytic monochlorination using 5a.
Scheme 24: Monofluorination using QuCN-ClO4 (8).
Scheme 25: Fluorination with fluorine-18.
Scheme 26: Aerobic amination with acridinium catalyst 3a.
Figure 24: Plausible mechanism for the aerobic amination using acridinium catalyst 3a.
Scheme 27: Aerobic aminations with semiconductor photoredox catalyst 18.
Scheme 28: Perfluoroalkylation of arenes.
Scheme 29: Synthesis of benzonitriles in the presence of 3a.
Figure 25: Plausible mechanism for the synthesis of substituted benzonitrile derivatives in the presence of 3a....
Synthesis of acremines A, B and F and studies on the bisacremines
- Nils Winter and
- Dirk Trauner
Beilstein J. Org. Chem. 2019, 15, 2271–2276, doi:10.3762/bjoc.15.219
- undergo Diels–Alder reactions with electron-rich dienophiles [13][14][15][16][17], treatment of 5 with Fukuzumi’s catalyst [18] under illumination with blue light only led to decomposition of the starting material (Table 1, entry 15). Notably, a photoredox catalyst with a lower oxidation potential could
Graphical Abstract
Figure 1: Selected members of the acremine family [3-5].
Scheme 1: Retrosynthetic analysis of acremine F (5).
Scheme 2: Total synthesis of acremine F (5).
Scheme 3: Synthesis of acremines A and B through selective oxidation of acremine F.
Scheme 4: Proposed biomimetic dimerization of 5.
Scheme 5: Attempted intramolecular cyclization of 23.
Scheme 6: Attempted photochemical cyclization of 25.
Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups
- Xiaowei Li,
- Xiaolin Shi,
- Xiangqian Li and
- Dayong Shi
Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218
- co-workers [117] explored a simple and facile method to access δ-trifluoromethylated carboxamides and sulfonamides through a copper-catalyzed 1,5-hydrogen atom transfer (Scheme 58). Other catalysts: In 2013, Gouverneur and co-workers [118] described a photoredox-based catalytic approach to afford
- oxidative decarboxylation. Then, Cu(CF3)2 provides a CF3 group to alkyl radicals to obtain the final product. Very recently, MacMillan et al. [120] discovered an efficient approach to the decarboxylative trifluoromethylation of aliphatic carboxylic acids via the combination of photoredox and copper
- catalysis (Scheme 61). The method tolerates a myriad of primary, secondary and tertiary carboxylic acids and provides the corresponding CF3 analogue in good to excellent yields. Details of the proposed dual copper–photoredox cycle are shown in Scheme 61. The Ir(III) photocatalyst Ir[dF(CF3)ppy]2(4,4
Graphical Abstract
Scheme 1: The main three strategies of fluorination: nucleophilic, electrophilic and radical fluorination.
Scheme 2: Doyle’s Pd-catalyzed fluorination of allylic chlorides.
Scheme 3: Allylic fluorination of 2- and 3-substituted propenyl esters.
Scheme 4: Regioselective allylic fluorination of cinnamyl phosphorothioate esters.
Scheme 5: Palladium-catalyzed aliphatic C–H fluorination reported by Doyle.
Scheme 6: Pd-catalyzed enantioselective fluorination of α-ketoesters followed by stereoselective reduction to...
Scheme 7: Pd-catalyzed C(sp3)–H fluorination of oxindoles.
Scheme 8: C–H fluorination of 8-methylquinoline derivatives with F− reagents.
Scheme 9: Fluorination of α-cyano acetates reported by van Leeuwen.
Scheme 10: The catalytic enantioselective electrophilic C–H fluorination of α-chloro-β-keto phosphonates.
Scheme 11: Fluorination of unactivated C(sp3)–H bonds directed by the bidentate PIP auxiliary.
Scheme 12: Fluorination of C(sp3)–H bonds at the β-position of carboxylic acids.
Scheme 13: Enantioselective benzylic C–H fluorination with a chiral transient directing group.
Scheme 14: Microwave-heated Pd-catalyzed fluorination of aryl alcohols.
Scheme 15: Fluorination of aryl potassium trifluoroborates.
Scheme 16: C(sp2)–F bond formation using precatalyst [L·Pd]2(cod).
Scheme 17: Pd-catalyzed fluorination of (hetero)aryl triflates and bromides.
Scheme 18: The Pd-catalyzed C–H fluorination of arenes with Selectfluor/NFSI.
Scheme 19: Pd(II)-catalyzed ortho-monofluorination protocol for benzoic acids.
Scheme 20: Pd-catalyzed C(sp2)–H bond fluorination of 2-arylbenzothiazoles.
Scheme 21: Nitrate-promoted fluorination of aromatic and olefinic C(sp2)–H bonds and proposed mechanism.
Scheme 22: Fluorination of oxalyl amide-protected benzylamine derivatives.
Scheme 23: C–H fluorination of benzaldehydes with orthanilic acids as transient directing group.
Scheme 24: Pd(II)-catalyzed aryl C–H fluorination with various directing groups.
Scheme 25: Cu-catalyzed aliphatic, allylic, and benzylic fluorination.
Scheme 26: Cu-catalyzed SN2 fluorination of primary and secondary alkyl bromides.
Scheme 27: Copper-catalyzed fluorination of alkyl triflates.
Scheme 28: Cu-catalyzed fluorination of allylic bromides and chlorides.
Scheme 29: Synthetic strategy for the fluorination of active methylene compounds.
Scheme 30: Fluorination of β-ketoesters using a tartrate-derived bidentate bisoxazoline-Cu(II) complex.
Scheme 31: Highly enantioselective fluorination of β-ketoesters and N-Boc-oxindoles.
Scheme 32: Amide group-assisted site-selective fluorination of α-bromocarbonyl compounds.
Scheme 33: Cu-mediated aryl fluorination reported by Sanford [77].
Scheme 34: Mono- or difluorination reactions of benzoic acid derivatives.
Scheme 35: Cu-catalyzed fluorination of diaryliodonium salts with KF.
Scheme 36: Copper(I)-catalyzed cross-coupling of 2-pyridylaryl bromides.
Scheme 37: AgNO3-catalyzed decarboxylative fluorination of aliphatic carboxylic acids.
Scheme 38: The Mn-catalyzed aliphatic and benzylic C–H fluorination.
Scheme 39: Iron(II)-promoted C–H fluorination of benzylic substrates.
Scheme 40: Ag-catalyzed fluorodecarboxylation of carboxylic acids.
Scheme 41: Vanadium-catalyzed C(sp3)–H fluorination.
Scheme 42: AgNO3-catalyzed radical deboronofluorination of alkylboronates and boronic acids.
Scheme 43: Selective heterobenzylic C–H fluorination with Selectfluor reported by Van Humbeck.
Scheme 44: Fe(II)-catalyzed site-selective fluorination guided by an alkoxyl radical.
Scheme 45: Fluorination of allylic trichloroacetimidates reported by Nguyen et al.
Scheme 46: Iridium-catalyzed fluorination of allylic carbonates with TBAF(t-BuOH)4.
Scheme 47: Iridium-catalyzed asymmetric fluorination of allylic trichloroacetimidates.
Scheme 48: Cobalt-catalyzed α-fluorination of β-ketoesters.
Scheme 49: Nickel-catalyzed α-fluorination of various α-chloro-β-ketoesters.
Scheme 50: Ni(II)-catalyzed enantioselective fluorination of oxindoles and β-ketoesters.
Scheme 51: Scandium(III)-catalyzed asymmetric C–H fluorination of unprotected 3-substituted oxindoles.
Scheme 52: Iron-catalyzed directed C–H fluorination.
Scheme 53: Electrophilic silver-catalyzed Ar–F bond-forming reaction from arylstannanes.
Figure 1: Nucleophilic, electrophilic and radical CF3 sources.
Scheme 54: Cu(I)-catalyzed allylic trifluoromethylation of unactivated terminal olefins.
Scheme 55: Direct copper-catalyzed trifluoromethylation of allylsilanes.
Scheme 56: Cupper-catalyzed enantioselective trifluoromethylation of five and six-membered ring β-ketoesters.
Scheme 57: Cu-catalyzed highly stereoselective trifluoromethylation of secondary propargyl sulfonates.
Scheme 58: Remote C(sp3)–H trifluoromethylation of carboxamides and sulfonamides.
Scheme 59: Trifluoromethylation of allylsilanes with photoredox catalysis.
Scheme 60: Ag-catalyzed decarboxylative trifluoromethylation of aliphatic carboxylic acids in aqueous CH3CN.
Scheme 61: Decarboxylative trifluoromethylation of aliphatic carboxylic acids via combined photoredox and copp...
Scheme 62: Palladium-catalyzed Ar–CF3 bond-forming reaction.
Scheme 63: Palladium-catalyzed trifluoromethylation of arenes with diverse heterocyclic directing groups.
Scheme 64: Pd-catalyzed trifluoromethylation of indoles as reported by Liu.
Scheme 65: Pd-catalyzed trifluoromethylation of vinyl triflates and vinyl nonaflates.
Scheme 66: Pd(II)-catalyzed ortho-trifluoromethylation of aromatic C–H bonds.
Scheme 67: Visible-light-induced Pd(OAc)2-catalyzed ortho-trifluoromethylation of acetanilides with CF3SO2Na.
Scheme 68: CuI-catalyzed trifluoromethylation of aryl- and alkenylboronic acids.
Scheme 69: Cu-catalyzed trifluoromethylation of aryl- and vinylboronic acids.
Scheme 70: Copper-catalyzed trifluoromethylation of α,β-unsaturated carboxylic acids.
Scheme 71: Formation of C(sp2)–CF3 bond catalyzed by copper(I) complex.
Scheme 72: Loh’s Cu(I)-catalyzed trifluoromethylation of enamides and electron-deficient alkenes.
Scheme 73: Copper and iron-catalyzed decarboxylative tri- and difluoromethylation.
Scheme 74: Cu-catalyzed trifluoromethylation of hydrazones developed by Bouyssi.
Scheme 75: Cu(I)-catalyzed trifluoromethylation of terminal alkenes.
Scheme 76: Cu/Ag-catalyzed decarboxylative trifluoromethylation of cinnamic acids.
Scheme 77: Copper-catalyzed direct alkenyl C–H trifluoromethylation.
Scheme 78: Copper(I/II)-catalyzed direct trifluoromethylation of styrene derivatives.
Scheme 79: Regioselective trifluoromethylation of pivalamido arenes and heteroarenes.
Scheme 80: Synthesis of trifluoromethylquinones in the presence of copper(I).
Scheme 81: Oxidative trifluoromethylation of imidazoheterocycles in ionic liquid/water.
Scheme 82: A mild and fast continuous-flow trifluoromethylation of coumarins using a CuI/CF3SO2Na/TBHP system.
Scheme 83: Copper-catalyzed oxidative trifluoromethylation of various 8-aminoquinolines.
Scheme 84: PA-directed copper-catalyzed trifluoromethylation of anilines.
Scheme 85: Trifluoromethylation of potassium vinyltrifluoroborates catalyzed by Fe(II).
Scheme 86: Alkenyl trifluoromethylation catalyzed by Ru(phen)3Cl2 as photocatalyst.
Scheme 87: Ru-catalyzed trifluoromethylation of alkenes by Akita’s group.
Scheme 88: Ir-catalyzed Cvinyl–CF3 bond formation of α,β-unsaturated carboxylic acids.
Scheme 89: Ag(I)-catalyzed denitrative trifluoromethylation of β-nitrostyrenes.
Scheme 90: Photocatalyzed direct trifluoromethylation of aryl and heteroaryl C–H bonds.
Scheme 91: Rhenium (MTO)-catalyzed direct trifluoromethylation of aromatic substrates.
Scheme 92: Trifluoromethylation of unprotected anilines under [Ir(ppy)3] catalyst.
Scheme 93: Oxidative trifluoromethylation of imidazopyridines and imidazoheterocycles.
Scheme 94: Ruthenium-catalyzed trifluoromethylation of (hetero)arenes with trifluoroacetic anhydride.
Scheme 95: Phosphovanadomolybdic acid-catalyzed direct C–H trifluoromethylation.
Scheme 96: Picolinamide-assisted ortho-trifluoromethylation of arylamines.
Scheme 97: A nickel-catalyzed C–H trifluoromethylation of free anilines.
Scheme 98: Cu-mediated trifluoromethylation of terminal alkynes reported by Qing.
Scheme 99: Huang’s C(sp)–H trifluoromethylation using Togni’s reagent.
Scheme 100: Cu-catalyzed methods for trifluoromethylation with Umemoto’s reagent.
Scheme 101: The synthesis of alkynyl-CF3 compounds in the presence of fac-[Ir(ppy)3] under visible-light irradi...
Scheme 102: Pd-catalyzed Heck reaction reported by Reutrakul.
Scheme 103: Difluoromethylation of enamides and ene-carbamates.
Scheme 104: Difluoromethylation of α,β-unsaturated carboxylic acids.
Scheme 105: Copper-catalyzed direct C(sp2)–H difluoroacetylation reported by Pannecoucke and co-workers.
Scheme 106: Difluoroalkylation of aldehyde-derived hydrazones with functionalized difluoromethyl bromides.
Scheme 107: Photoredox-catalyzed C–H difluoroalkylation of aldehyde-derived hydrazones.
Scheme 108: Synergistic ruthenium(II)-catalyzed C–H difluoromethylation reported by Ackermann.
Scheme 109: Visible-light photocatalytic decarboxylation of α,β-unsaturated carboxylic acids.
Scheme 110: Synthesis of difluorinated ketones via S-alkyl dithiocarbamates obtained from acyl chlorides and po...
Scheme 111: Synthesis of aryl and heteroaryl difluoromethylated phosphonates.
Scheme 112: Difluoroalkylation of secondary propargyl sulfonates using Cu as the catalyst.
Scheme 113: Ru(II)-mediated para-selective difluoromethylation of anilides and their derivatives.
Scheme 114: Bulky diamine ligand promoted cross-coupling of difluoroalkyl bromides.
Scheme 115: Copper-catalyzed C3–H difluoroacetylation of quinoxalinones.
Scheme 116: Copper(I) chloride-catalyzed trifluoromethylthiolation of enamines, indoles and β-ketoesters.
Scheme 117: Copper-boxmi-catalyzed asymmetric trifluoromethylthiolation of β-ketoesters.
Scheme 118: Direct Cu-catalyzed trifluoromethylthiolation of boronic acids and alkynes.
Scheme 119: Cu-catalyzed synthesis of α-trifluoromethylthio-substituted ketones.
Scheme 120: Trifluoromethylthiolation reactions promoted by diazotriflone and copper.
Scheme 121: Halide activation of N-(trifluoromethylthio)phthalimide.
Scheme 122: The visible light-promoted trifluoromethylthiolation reported by Glorius.
Scheme 123: Synthesis of α-trifluoromethylthioesters via Goossen’s approach.
Scheme 124: Photoinduced trifluoromethylthiolation of diazonium salts.
Scheme 125: Ag-mediated trifluoromethoxylation of aryl stannanes and arylboronic acids.
Scheme 126: Catalytic (hetero)aryl C–H trifluoromethoxylation under visible light.
Scheme 127: Photoinduced C–H-bond trifluromethoxylation of (hetero)arenes.
Friedel–Crafts approach to the one-pot synthesis of methoxy-substituted thioxanthylium salts
- Kenta Tanaka,
- Yuta Tanaka,
- Mami Kishimoto,
- Yujiro Hoshino and
- Kiyoshi Honda
Beilstein J. Org. Chem. 2019, 15, 2105–2112, doi:10.3762/bjoc.15.208
- . Keywords: Friedel–Crafts reaction; metal-free conditions; one-pot synthesis; photoredox catalyst; thioxanthylium salt; Introduction Thioxanthylium salts are one of the important structural motifs found in biologically active compounds and photochemical materials [1][2][3][4][5][6][7][8]. Owing to these
Graphical Abstract
Scheme 1: The representative synthesis of thioxanthylium salts.
Figure 1: The generality of diaryl sulfide 1 and benzoyl chloride 2. aThe reaction was carried out with 1a (2...
Figure 2: The UV–vis spectra of thioxanthylium salt (0.1 mM) in CH3CN.
Figure 3: Frontier orbitals of thioxanthylium salts, calculated by DFT at the B3LYP/6-31G(d,p) level of Orca....
Figure 4: UV–vis spectra of thioxanthylium salts 3b and 4b (0.1 mM) in CH3CN.
Figure 5: Structure of thioxanthylium salt 4.
Figure 6: Cyclic voltammograms of thioxanthylium salts 3b and 4b.
Naphthalene diimides with improved solubility for visible light photoredox catalysis
- Barbara Reiß and
- Hans-Achim Wagenknecht
Beilstein J. Org. Chem. 2019, 15, 2043–2051, doi:10.3762/bjoc.15.201
- light photoredox catalysts and characterized by methods of optical spectroscopy and electrochemistry in comparison with one unsubstituted naphthalene diimide as reference. The core-substituted naphthalene diimides differ by the alkyl groups at the imide nitrogens and at the nitrogens of the two
- substituents at the core in order to enhance their solubility in DMF and thereby enhance their photoredox catalytic potential. The 1-ethylpropyl group as rather short and branched alkyl substituent at the imide nitrogen and the n-propyl group as short and unbranched one at the core amines yielded the best
- potential was estimated to be approximately +1.0 V (vs SCE) which is sufficient to photocatalyze typical organic reactions. The photoredox catalytic activity in the visible light range was tested by the α-alkylation of 1-octanal as benchmark reaction. Irradiations were performed with LEDs in the visible
Graphical Abstract
Scheme 1: Synthesis of reference NDI 1 and cNDIs 2–6; bottom: image of saturated solutions of cNDIs 2–6 in DM...
Figure 1: Optical properties of NDI 1 and cNDIs 2 and 6: UV–vis absorbance in CH2Cl2 and in DMF (normal lines...
Scheme 2: Photocatalytic α-alkylation of octanal (12): 500 mM 12, 250 mM 13, 50 mM (20 mol %) organocatalyst ...
Figure 2: Normalized absorbance of cNDI 6 in comparison to normalized emission of the 468 nm, 520 nm, 597 nm,...
Figure 3: Kinetic analysis of yields of product 14 in the presence (solid lines) and in the absence (dashed l...
A review of the total syntheses of triptolide
- Xiang Zhang,
- Zaozao Xiao and
- Hongtao Xu
Beilstein J. Org. Chem. 2019, 15, 1984–1995, doi:10.3762/bjoc.15.194
- trimethylsilyl trifluoromethanesulfonate (TMSOTf) in a diastereoselective and stepwise manner. This novel methodology provides a shorter access to the intermediate 97, which is a key intermediate for the synthesis of triptolide. Recently, photoredox catalysis has emerged as a powerful and high-yielding method
- oxidation of the tertiary radical and reduction of the [Au-Au]3+ ion could give the cyclization product and regenerate the dimeric gold photocatalyst. Later, the utility of this photoredox methodology was demonstrated in a concise formal synthesis of triptolide (1) via the reaction of bromobutenolide 19
- under the optimal photoredox conditions to provide tetracyclic intermediate 19i (dr = 1:1, Scheme 8, route L), with a cis A-/B-ring connection rather than the desired trans connection. Treatment of 19i with H2SO4, followed by RuCl2(PPh3)3-catalyzed double bond isomerization gave the known intermediate
Graphical Abstract
Figure 1: Structures of triptolide (1), triptonide (2), tripdiolide (3), 16-hydroxytriptolide (4), triptrioli...
Figure 2: Syntheses of triptolide.
Scheme 1: Berchtold’s synthesis of triptolide.
Scheme 2: Li’s formal synthesis of triptolide.
Scheme 3: van Tamelen’s asymmetric synthesis of triptonide and triptolide.
Scheme 4: Van Tamelen’s (method II) formal synthesis of triptolide.
Scheme 5: Sherburn’s formal synthesis of triptolide.
Scheme 6: van Tamelen’s biogenetic type total synthesis of triptolide.
Scheme 7: Yang’s total synthesis of triptolide.
Scheme 8: Key intermediates or transformations of routes J–N.
Tandem copper and photoredox catalysis in photocatalytic alkene difunctionalization reactions
- Nicholas L. Reed,
- Madeline I. Herman,
- Vladimir P. Miltchev and
- Tehshik P. Yoon
Beilstein J. Org. Chem. 2019, 15, 351–356, doi:10.3762/bjoc.15.30
- describe a method for alkene oxyamination and diamination that utilizes simple carbamate and urea groups as nucleophilic heteroatom donors. This method uses a tandem copper–photoredox catalyst system that is operationally convenient. The identity of the terminal oxidant is critical in these studies. Ag(I
- ) salts proved to be unique in their ability to turn over the copper cocatalyst without deleteriously impacting the reactivity of the organoradical intermediates. Keywords: copper; diamination; oxidative functionalization; oxyamination; photoredox catalysis; radical; Introduction Over the past decade, a
- photoinduced electron transfer processes. A major theme of research that has emerged from these studies is the application of various cocatalysts to intercept the organoradical intermediates of photoredox reactions and modulate their subsequent reactivity [5][6]. The combination of photoredox catalysis with
Graphical Abstract
Figure 1: a) Photocatalytic oxyamination, b) photocatalytic diamination, and c) proposed mechanism for photoc...
Figure 2: Scope studies for dual-catalytic alkene difunctionalization using 2.5 mol % 3, 30 mol % Cu(TFA)2, a...
