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

• occurring on a stilbene diazonium salt (e.g., 1.1+) with the intermediacy of an aryl radical [40]. Alternative strategies for the synthesis of phenanthrenes have been later reported, including the adoption of [4 + 2] benzannulations between biaryl derivatives and alkynes [41][42]. Scheme 2 illustrates one

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118

• used similar disulfide-catalyzed [3 + 2] cycloaddition reactions for the synthesis of polycyclic frameworks. The irradiation of vinylcyclopropanes with alkenes or alkynes in the presence of dibutyl disulfide afford the desired bi- or tricyclic products with 54–88% yield (Scheme 2) [6]. In 2014, Maruoka

• also catalyze the formation of four-membered ring intermediates between double or triple bonds and oxygen, and thus converting unsaturated hydrocarbons to carbonyl compounds. Regarding the oxidation of alkynes, Wang reported a method for preparing diaryl-1,2-diketones from diarylalkynes in the presence

• groups that contain heteroatoms. Ogawa and co-workers reported a class of efficient diboration reactions. Under light irradiation, disulfide was used as the photocatalyst to facilitate the addition of bis(pinacolato)diboron (B2pin2) to terminal alkynes [19], and the corresponding diboryl alkenes were

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

• alkynes. They can also perform atom abstractions, in particular HATs and halogen abstractions [66]. The generation of such species generally occurs through the homolytic cleavage of a peripheral σ bond [67][68]. In the majority of the cases, a leaving group is reduced and fragments to the aryl radical

• class of substrates that usually undergo a protonation to form C(sp3) radicals. Alkenyl or aryl radical ions are generally accessed through SET. The presence of electron-donating groups facilitates the oxidation of the precursor to the radical cations, while electron-poor alkynes and arenes can undergo

• reaction (Scheme 23) [100]. The alkynes 23.1 could be successfully converted to the vinyl sulfones 23.3 in the presence of the aryl sulfones 23.2 using eosin Y (OD13) as a photocatalyst. A tentative mechanism was proposed by the authors: under visible-light irradiation, the arylsulfinic acid could be

Palladium-catalyzed regio- and stereoselective synthesis of aryl and 3-indolyl-substituted 4-methylene-3,4-dihydroisoquinolin-1(2H)-ones

• Valeria Nori,
• Antonio Arcadi,
• Armando Carlone,
• Fabio Marinelli and
• Marco Chiarini

Beilstein J. Org. Chem. 2020, 16, 1084–1091, doi:10.3762/bjoc.16.95

• antimetastatic agents [14]. Fittingly, the development of efficient strategies for their construction and peripheral functionalization represents still an active research area aimed to achieve structural diversity [15][16][17][18]. Carbometalations of alkynes constitute a powerful tool for the regio- and

• functionalized alkynes with boronic acids [32][33] prompted us to explore the palladium-catalyzed reaction of the readily available alkynyliodobenzamides 2 with boronic acids 3 as a viable route to the regio- and stereoselective synthesis of 4-alkylidene-3,4-dihydroisoquinolin-1(2H)-ones 3 (Scheme 1a). We are

Copper-based fluorinated reagents for the synthesis of CF₂R-containing molecules (R ≠ F)

• Louise Ruyet and
• Tatiana Besset

Beilstein J. Org. Chem. 2020, 16, 1051–1065, doi:10.3762/bjoc.16.92

• functionalization of alkyl bromides, alkyl mesylates, aryldiazonium salts [43] as well as electron-rich arenes [44] (Scheme 4). In 2015, the group of Qing investigated the oxidative difluoromethylation reaction of terminal alkynes with TMSCF2H via a copper-mediated reaction [45]. Using a stoichiometric amount of

• CuI, in the presence of t-BuOK and 9,10-phenanthraquinone, the functionalization of a panel of (hetero)aromatic and aliphatic terminal alkynes was achieved (Scheme 5). A good functional group tolerance was observed as alkynes bearing a cyano, ester, bromo or amino group among others were suitable

• substrates. Based on 19F NMR studies, the authors suggested the following mechanism: first the in situ generation of a CuCF2H complex from TMSCF2H in equilibrium with the corresponding cuprate (Cu(CF2H)2−) occurred followed by the reaction with terminal alkynes under basic conditions. The resulting

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

• ). For an oxidative quenching, the photoarylation of heteroarenes and alkynes with aryldiazonium salts, and the oxidative decarboxylative coupling between cinnamic acid and tetrahydrofuran also showed better results when NiTPP was used instead of eosin [32][33][34] (Scheme 10). Regarding protocols

• hydration of terminal alkynes to ketones can be photocatalyzed by rhodium(III) tetrakis(p-sulfonylphenyl)porphyrin (RhIIITSPP) [37]. The coupling between RhIII(TSPP) and terminal alkynes produced the β-carbonylalkylrhodium porphyrin as a photoactive intermediate, whose irradiation produced the PhCOCH2

• tetrahydroquinolines by reductive quenching. Selenylation and thiolation of anilines. NiTPP as photoredox catalyst in oxidative and reductive quenching, in comparison with other photocatalysts. C–O bond cleavage of 1-phenylethanol using a cobalt porphyrin (CoTMPP) under visible light. Hydration of terminal alkynes by

Copper catalysis with redox-active ligands

• Agnideep Das,
• Yufeng Ren,
• Cheriehan Hessin and
• Marine Desage-El Murr

Beilstein J. Org. Chem. 2020, 16, 858–870, doi:10.3762/bjoc.16.77

• wide variety of substrates including silyl enol ethers, heteroaromatics and alkynes using an electrophilic CF3+ source (8 or 9), opening new opportunities to access pharmaceutically relevant trifluoromethylated products under mild reaction conditions. The ligand-based SET step involved the

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• decade later, Molander et al. made use of the same disilane as a source of the nucleophile for additions to α,β-unsaturated alkenes and alkynes as Michael acceptors bearing sulfones, nitriles, cyano, amido, and carboxyl ester groups to form β-silylated alkanes and alkenes in good to moderate yields [55

• , could be intercepted at the intermediate radical stage (149) with radical initiator TBHP present in excess, leading to silylated peroxy products 151–156. This approach was applied to different types of conjugated systems, including esters, ketones, amides, alkynes, etc. (Scheme 27). Kleeberg [64] et al

• bond formation Organoboron compounds are widely used in C–C and C–X (X = N, O) bond constructions. Straightforward methods for their synthesis involve the copper-catalyzed addition of organoboron compounds to alkynes, alkenes, and unsaturated carbonyl compounds, as well as the nucleophilic borylation

Cascade trifluoromethylthiolation and cyclization of N-[(3-aryl)propioloyl]indoles

• Ming-Xi Bi,
• Shuai Liu,
• Yangen Huang,
• Xiu-Hua Xu and
• Feng-Ling Qing

Beilstein J. Org. Chem. 2020, 16, 657–662, doi:10.3762/bjoc.16.62

• the direct incorporation of the SCF3 group into organic compounds [9][10][11][12][13][14][15][16], such as alkynes, alkenes, arenes, and alkanes. Despite these impressive advances, there is a continued strong demand for new methods that enable the efficient synthesis of SCF3-containing compounds

• strategy in the synthesis of a series of CH2SCF3-substituted heterocycles. For the construction of SCF3-substituted cyclic compounds, normally proper alkynes are chosen as the substrates for cascade reactions [28][29][30][31][32]. In 2015, Wang developed an oxidative radical cyclization of aryl alkynoate

Copper-catalyzed O-alkenylation of phosphonates

• Nuria Vázquez-Galiñanes,
• Mariña Andón-Rodríguez,
• Patricia Gómez-Roibás and
• Martín Fañanás-Mastral

Beilstein J. Org. Chem. 2020, 16, 611–615, doi:10.3762/bjoc.16.56

• counterparts has received less attention. Current methodologies for the synthesis of acyclic mixed enol phosphonates include the Perkow-type reaction between phosphonites and α-halocarbonyl compounds [11], the mercury-catalyzed addition of phosphonic acid monoesters to terminal alkynes [12][13] and multistep

A systematic review on silica-, carbon-, and magnetic materials-supported copper species as efficient heterogeneous nanocatalysts in “click” reactions

• Pezhman Shiri and
• Jasem Aboonajmi

Beilstein J. Org. Chem. 2020, 16, 551–586, doi:10.3762/bjoc.16.52

• oxidized to Cu(II) species. Without using a ligand or a reducing agent, Cu(II) can oxidize alkynes to produce an undesired byproduct. Active copper catalysts can be prepared by reducing copper(II) sources, oxidizing copper metal, comproportionation of Cu(II) and Cu(0), or combination of copper salts and

• -functionalized silica 46 was added to the mixture, and this was heated to reflux to generate the catalyst 48. Several organic halides or epoxides, nonactivated alkynes, and sodium azide were reacted in an aqueous medium to provide triazoles or β-hydroxytriazoles using 1.0 mol % catalyst loading at 25 °C

• reflux conditions for one day. The resulting powder was filtered off, washed with methanol, and dried. Finally, excess copper was removed by the Soxhlet extraction method (Scheme 9). The 1,3-dipolar reaction of organic alkynes, organic bromides (or aryldiazonium salts or epoxides), and sodium azide

Controlling alkyne reactivity by means of a copper-catalyzed radical reaction system for the synthesis of functionalized quaternary carbons

• Goki Hirata,
• Yu Yamane,
• Naoya Tsubaki,
• Reina Hara and
• Takashi Nishikata

Beilstein J. Org. Chem. 2020, 16, 502–508, doi:10.3762/bjoc.16.45

• ; Introduction Terminal alkynes are undoubtedly useful functional groups for organic synthesis, and they can undergo a variety of reactions [1]. The C–C triple bond of an alkyne is suitable for addition reactions, whereas the terminal hydrogen atom is a good target for cross-coupling by using Sonogashira and

• related coupling reactions [2][3][4]. Although there are many reports on alkyne transformations, one recent development in this area has been the reaction of alkynes with tertiary alkyl electrophiles to produce functionalized quaternary carbon atoms via addition [5][6][7][8][9][10] or coupling [11][12][13

• ][14][15][16]. Recently, we have prepared quaternary carbon centers via radical reactions by using α-bromocarbonyl compounds (a tertiary alkyl source) and olefins or heteroatoms in the presence of a copper catalyst [17][18][19]. During our studies, we found that combinations of alkynes and tertiary

Aerobic synthesis of N-sulfonylamidines mediated by N-heterocyclic carbene copper(I) catalysts

• Faïma Lazreg,
• Marie Vasseur,
• Alexandra M. Z. Slawin and
• Catherine S. J. Cazin

Beilstein J. Org. Chem. 2020, 16, 482–491, doi:10.3762/bjoc.16.43

• area, reporting on the synthesis of the first heteroleptic bis-NHC and mixed NHC/phosphine copper(I) complexes [20][21][22]. Interestingly, these new copper-based complexes have shown excellent activity in the [3 + 2] cycloaddition reaction of azides/sulfonyl azides and alkynes (Scheme 1, right) [22

• . Various terminal aryl/alkyl-substituted alkynes were investigated in the presence of tosyl azide and diisopropylamine (Scheme 4). Under standard conditions, good to excellent yields were obtained. The presence of functional groups in para-position of the aryl ring leads to a decrease of the conversion to

• substrate, solvent-free conditions lead to 78% isolated yield at 40 °C. Diynes were also investigated and excellent isolated yields were achieved (92% and 85% for 11j and 11k, respectively). Regarding the alkyl-alkynes, longer reactions times as well as higher temperature were required to reach high

Recent advances in photocatalyzed reactions using well-defined copper(I) complexes

• Mingbing Zhong,
• Xavier Pannecoucke,
• Philippe Jubault and
• Thomas Poisson

Beilstein J. Org. Chem. 2020, 16, 451–481, doi:10.3762/bjoc.16.42

• alkynes. [Cu(I)(dap)2]Cl was found to be the best catalyst for this transformation proceeding upon irradiation at 530 nm (green LED, Scheme 6) [22]. Indeed, the comparison of this Cu catalyst with [Ru(bpy)3]Cl2 and Ir(ppy)3 clearly demonstrated the higher efficiency, good yield, selectivity, and excellent

• of the ligand iodide for DAP (path III). Another possibility was the trapping of the radical with the iodine ligand of the [Cu(II)] catalyst (path IV). In 2019, Reiser’s group described a chlorosulfonylation reaction of alkenes and alkynes with [Cu(I)(dap)2]Cl or [Cu(II)(dap)2]Cl2 under visible light

• chlorosulfonylation of terminal alkenes and alkynes using the previously developed copper-based photocatalyst (Scheme 19) [35]. The reaction was tolerant to a broad range of arylchlorosulfonyl derivatives when the reaction was carried out with styrene, including sterically hindered and heteroaromatic substrates

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

Copper-promoted/copper-catalyzed trifluoromethylselenolation reactions

• Clément Ghiazza and
• Anis Tlili

Beilstein J. Org. Chem. 2020, 16, 305–316, doi:10.3762/bjoc.16.30

• could be trifluoromethylselenolated that way (Scheme 2) [13][15][16][17]. Mechanistically, the authors postulated the involvement of copper(I)/(III) oxidation states. Oxidative cross-coupling reactions between terminal alkynes using the [(bpy)CuSeCF3]2 complex were also undertaken by the same group to

• reagent was involved in several cross-coupling processes, including copper chemistry. In this context, in 2015, the group of Rueping reported an oxidative trifluoromethylselenolation process of terminal alkynes and boronic acid derivatives (Scheme 10) [27]. Using a stoichiometric amount of copper/ligand

• ClSeCF3 is generated in situ [33]. This strategy was then applied to the trifluoromethylselenolation of alkynes by using copper(I) acetylides [34]. With bipyridine as the ligand, the trifluoromethylselenolation of alkynes was reported to occur with moderate to very good yields. The conditions were

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

• scaffolds in their structures [104][105][106][107]. By employing dual photoredox catalysis, in 2016, Fabry et al. reported the cyclization of substituted anilides with alkynes to produce indoles [108]. Unlike previously reported syntheses, viz, an indole synthesis by the Fagnou group utilizing a large

• thiolation. Synthesis of indoles via C–H cyclization of anilides with alkynes. Preparation of 3-trifluoromethylcoumarins via C–H cyclization of arylpropiolate esters. Monobenzoyloxylation without chelation assistance. Aryl-substituted arenes prepared by inorganic photoredox catalysis using 12a. Arylation of

Combination of multicomponent KA² and Pauson–Khand reactions: short synthesis of spirocyclic pyrrolocyclopentenones

• Riccardo Innocenti,
• Elena Lenci,
• Gloria Menchi and
• Andrea Trabocchi

Beilstein J. Org. Chem. 2020, 16, 200–211, doi:10.3762/bjoc.16.23

• basic nitrogen atoms [28]. The variation of the alkyne component proved to give the KA2 coupling adduct when aromatic terminal alkynes were used, as shown in Table 1, entries 1 and 2 for those containing phenyl and thienyl moieties, resulting in 82% and 74% yield for the KA2 step. Subsequent acylation

• and pairing steps proved to proceed in good yield, thus furnishing the corresponding spirocyclopentenone derivatives 5 and 9 with an aromatic appendage at the carbonyl alpha carbon. On the contrary, when aliphatic alkynes were applied in the KA2 process, no reaction with allylamine and cyclohexanone

Extension of the 5-alkynyluridine side chain via C–C-bond formation in modified organometallic nucleosides using the Nicholas reaction

• Renata Kaczmarek,
• Dariusz Korczyński,
• James R. Green and
• Roman Dembinski

Beilstein J. Org. Chem. 2020, 16, 1–8, doi:10.3762/bjoc.16.1

• confirmed that the Nicholas reaction can be carried out in a nucleoside presence, leading to a divergent synthesis of novel metallo-nucleosides enriched with alkene, arene, arylketo, and heterocyclic functions, in the deoxy and ribo series. Keywords: alkynes; 5-alkynyluridines; C–C-bond formation; dicobalt

Construction of trisubstituted chromone skeletons carrying electron-withdrawing groups via PhIO-mediated dehydrogenation and its application to the synthesis of frutinone A

• Qiao Li,
• Chen Zhuang,
• Donghua Wang,
• Wei Zhang,
• Rongxuan Jia,
• Fengxia Sun,
• Yilin Zhang and
• Yunfei Du

Beilstein J. Org. Chem. 2019, 15, 2958–2965, doi:10.3762/bjoc.15.291

• ][76][77], converting alkynes and alkenes to ketones [78], oxidizing alcohols to aldehydes [79][80], as well as in the direct α-hydroxylation of ketones [81]. Furthermore, it could also be used to realize oxidative C–C [82], C–N [83], and C–O [84] bond formations. However, to the best of our knowledge

Palladium-catalyzed Sonogashira coupling reactions in γ-valerolactone-based ionic liquids

• László Orha,
• József M. Tukacs,
• László Kollár and
• László T. Mika

Beilstein J. Org. Chem. 2019, 15, 2907–2913, doi:10.3762/bjoc.15.284

• the product isolation procedure. In addition, it is well-established that the presence of Cu(I) salt can promote the in situ formation of some Cu(I) acetylides, which can readily undergo oxidative homocoupling of alkynes even in their slight excess in the reaction mixture [15][38][39]. Thus, the

Influence of the cis/trans configuration on the supramolecular aggregation of aryltriazoles

• Sara Tejera,
• Giada Caniglia,
• Rosa L. Dorta,
• Andrea Favero,
• Javier González-Platas and
• Jesús T. Vázquez

Beilstein J. Org. Chem. 2019, 15, 2881–2888, doi:10.3762/bjoc.15.282

• "click" chemistry [16][17][18] of azides and alkynes catalyzed by Cu(I) salts, the CuAAC reaction. Self-assembling properties were not observed for any of the prepared monotriazoles, namely the 4-substituted 1-glucopyranosyltriazoles 1a–g and 2a–g (Scheme 1) [15]. However, most ditriazoles 7a–g and 8a–g

• from the corresponding alkynes and diazides 5 and 6, respectively. In this context, it was required to isolate 5 and 6 before the coupling reaction could be performed. Compounds 9 and 10 (Scheme 3) were obtained in good yields by treatment of 7f and 8f, respectively, with sodium methoxide in CH2Cl2

Iodine-mediated hydration of alkynes on keto-functionalized scaffolds: mechanistic insight and the regiospecific hydration of internal alkynes

• Zachary Lee,
• Brandon R. Jones,
• Nyochembeng Nkengbeza,
• Michael Phillips,
• Kayla Valentine,
• Alexis Stewart,
• Brandon Sellers,
• Nicholas Shuber and
• Karelle S. Aiken

Beilstein J. Org. Chem. 2019, 15, 2747–2752, doi:10.3762/bjoc.15.265

• hydration reaction of alkynes serves as a green alternative to metal-catalyzed procedures. Previous work has shown that this method works well with terminal alkynes on keto-functionalized scaffolds, including 1,3-dicarbonyls and their heteroatom analogues. It was hypothesized that the reaction proceeds

• through a 5-exo-dig neighboring group participation (NGP) cyclization and an α-iodo intermediate. The work described herein probes the existence of the intermediate through NMR investigations and explores the scope of the hydration process with internal alkynes. The NMR experiments confirm the existence

• of the α-iodo intermediate, and methodology studies demonstrate that alkyl-capped, asymmetric, internal alkynes undergo a regiospecific hydration, also via the 5-exo-dig NGP pathway. Keywords: α-iodo intermediate; internal alkyne; iodine-mediated hydration; neighboring group participation

Fluorinated maleimide-substituted porphyrins and chlorins: synthesis and characterization

• Valentina A. Ol’shevskaya,
• Elena G. Kononova and
• Andrei V. Zaitsev

Beilstein J. Org. Chem. 2019, 15, 2704–2709, doi:10.3762/bjoc.15.263

• 1,2,3-triazole heterocycles via the copper-catalyzed azide–alkyne cycloaddition reaction (CuAAC) between alkynes and azides, developed independently by Sharpless [41] and Meldal [42]. In addition to the applications of triazoles as pharmacophores in the potential biologically active molecules, these

Emission solvatochromic, solid-state and aggregation-induced emissive α-pyrones and emission-tuneable 1H-pyridines by Michael addition–cyclocondensation sequences

• Natascha Breuer,
• Irina Gruber,
• Christoph Janiak and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2019, 15, 2684–2703, doi:10.3762/bjoc.15.262

• -pyrones from acid chlorides, terminal alkynes and dialkyl malonates. Consecutive pseudo-four-component alkynylation–Michael addition–cyclocondensation (AMAC) synthesis of 1H-pyridines 5a and an aniline derivative. Consecutive pseudo-four-component alkynylation–Michael addition–cyclocondensation (AMAC

• ) synthesis of 1H-pyridines 5a from acid chlorides 1, terminal alkynes 2 and ethyl cyanoacetate (4). Model system for the optimization of the Michael addition–cyclocondensation reaction step to 1H-pyridine 5a or/and α-pyrone 6a. Formation of α-pyrone 6a and 1H-pyridine 5a at 20 °C. Formation of α-pyrone 6a