Natural photosynthesis is a remarkable chemical machinery that enables our life on earth and delivers a constant stream of oxygen and organic biomass. We should acknowledge this fact with humbleness, especially because we have not been able yet to mimic this process in a reliable way even after decades of intense research. The basic mechanistic principle behind photosynthesis is photoredox catalysis or light-driven charge separation, which leads to an energy harvesting process by taking advantage of the reduction products and filling the holes by a sacrificial electron donor, water. In contrast to the “traditional” catalysis areas such as metal-, organo- and biocatalysis, photoredox catalysis (and photocatalysis in general) is a young research field with regard to synthetic applications. The collection of papers in this Thematic Series on organic synthesis using photoredox catalysis shows this convincingly.
See also the Thematic Series:
Photocycloadditions and photorearrangements
Graphical Abstract
Scheme 1: Strategy for in situ generation of bromine.
Scheme 2: Synthesis of dibromophenol product 2b''.
Scheme 3: Scope of the photocatalytic bromination of alkenes.
Scheme 4: Bromination of diketones and cyclization reactions.
Graphical Abstract
Scheme 1: Examples of photoinitiating systems.
Figure 1: Previously reported PIC (based on metal complexes) [45-52].
Figure 2: Previously reported PIC (metal free organic molecules) [54,55].
Scheme 2: Reaction mechanisms for the three-component system PIC/eA/E-Z.
Scheme 3: Reaction mechanisms for the two-component system PIC/eA.
Scheme 4: Reaction mechanisms for the system PIC/eA/add.
Scheme 5: Reaction mechanisms for the system PIC/eD/B-Y.
Figure 3: Typical oxidation and reduction agents used through the photoredox catalysis approach in polymeriza...
Figure 4: Typical monomers that can be polymerized through a photoredox catalysis approach.
Scheme 6: Reaction mechanisms for the system Ru(bpy)32+/Ph2I+/R3SiH.
Scheme 7: Reaction mechanisms for the Ru(ligand)32+/Ph3S+/R3SiH system.
Scheme 8: Reaction mechanisms for the Ru(ligand)32+/Ph2I+/NVK system upon visible lights.
Scheme 9: Reaction mechanisms for the violanthrone/Ph2I+/TTMSS (R3SiH) system upon red lights.
Scheme 10: Reaction mechanisms for the Tr-AD/R-Br/MDEA system upon visible lights.
Scheme 11: The photoredox catalysis for controlled polymerization reactions.
Scheme 12: Reaction mechanisms for the Ru(ligand)32+/MDEA/R-Br system upon visible lights.
Scheme 13: Reaction mechanisms for the Violanthrone/Ru(ligand)32+/Ph2I+/R3SiH system upon visible lights.
Scheme 14: Reaction mechanisms for the MK/amine/triazine system upon visible lights.
Figure 5: The new proposed PIC (Ir(piq)2(tmd)).
Figure 6: UV–visible light absorption spectra for Ir(piq)2(tmd) (2) and Ir(ppy)3 (1); solvent: acetonitrile.
Figure 7: (A) cyclic voltamogramm for Ir(piq)2(tmd) in acetonitrile; (B) absorption (a) and luminescence (b) ...
Figure 8: Photolysis of a Ir(piq)2(tmd)/Ph2I+ solution ([Ph2I+] = 0.023 M, in acetonitrile) upon a halogen la...
Figure 9: ESR spin-trapping spectra for the irradiation of a Ir(piq)2(tmd)/Ph2I+ solution in the presence of ...
Figure 10: (A) Photopolymerization profile of EPOX; photoinitiating system: Ir(piq)2(tmd)/Ph2I+/NVK (1%/2%/3%)...
Figure 11: (A) Photopolymerization profile of TMPTA; initiating systems: (1) Ir(piq)2(tmd)/MDEA (1%/2%) and (2...
Graphical Abstract
Scheme 1: PET-catalyzed addition of N,N-dimethylaniline (1) to furan-2(5H)-one 2 [38] and of N-methyl-N-((trimeth...
Scheme 2: Ir-catalyzed formation of tricyclic product 10 by a domino radical addition reaction to α,β-unsatur...
Scheme 3: Ir-catalyzed addition reactions of N-methyl-N-((trimethylsilyl)methyl)aniline (5) to 5,6-dihydro-2H...
Scheme 4: Ir-catalyzed addition reactions of N-methyl-N-((trimethylsilyl)methyl)aniline (5) to 2-cyclopenteno...
Scheme 5: Ir-catalyzed formation of tricyclic products 19 by a domino radical addition reaction to α,β-unsatu...
Scheme 6: Ir-catalyzed addition reactions of N-methyl-N-((trimethylsilyl)methyl)aniline (5) to α,β-unsaturate...
Scheme 7: Ir-catalyzed addition reactions of N-methyl-N-((trimethylsilyl)methyl)aniline (5) to α,β-unsaturate...
Scheme 8: Cyclization of putative radical A to intermediate B competes with reduction of A to form addition p...
Graphical Abstract
Scheme 1: Chemical structures of RB, EDB and TA.
Scheme 2: Type II PIS mechanisms. PS: photosensitizer; 1,3PS*: singlet and triplet PS excited states; PS•+: o...
Figure 1: Evolution of RB concentration as a function of irradiation time (λ = 532 nm, 9 mW·cm−3); insert: ab...
Scheme 3: Photocatalytic behavior occurring in three component PIS. PS: photosensitizer; 1,3PS*: singlet and ...
Figure 2: Evolution of [RB](t) in the photocyclic system RB/TA/EDB as a function of irradiation time (λ = 532...
Scheme 4:
Thermodynamics of an oxidative three components PCIS, a) ground state reaction (), b) excited state...
Scheme 5: General photocatalytic cycle occurring in three components photocyclic systems. Two cycles are in c...
Figure 3: Mechanistic description of photocyclic system involved in the RB/TA/EDB system. The rate constants ...
Figure 4: Evolution of RB, RB•+, TA, and TA•− concentration with time for RB/TA system.
Figure 5: Evolution of RB, TA and EDB concentrations in the photocyclic system. The logarithm of oxidative an...
Figure 6: Evolution of radical concentrations TA•− and EDB•+ together with [RB] in photocatalytic system.
Graphical Abstract
Figure 1: Substrate scope.
Scheme 1: Synthesis of a fused indoline.
Scheme 2: Proposed catalytic cycle.
Graphical Abstract
Scheme 1: Oxidative quenching of eosin Y with arenediazonium salts and reactions of the resultant aryl radica...
Scheme 2: Proposed general reaction mechanism of eosin Y-catalyzed substitutions with arene diazonium salts.
Figure 1: UV–vis spectra of the photoborylation reaction mixture (RM).
Figure 2: Fluorescence spectra of the photoborylation reaction mixture (RM). Ex. = excitation wavelength.
Scheme 3: Acid–base behaviour of eosin Y.
Figure 3: UV–vis spectrum of p-bromobenzenediazonium tetrafluoroborate (pBrPhN2) and bispinacolato diboron (B2...
Scheme 4: Eosin Y-catalyzed and dye-free photolytic borylation.
Scheme 5: Eosin Y-catalyzed and dye-free reactions with ethyl propiolate.
Figure 4: UV–vis spectra of ortho-biphenyldiazonium tetrafluoroborate (biPhN2) in acetonitrile.
Scheme 6: Quantum yield determinations of selected visible-light-driven aromatic substitutions.
Graphical Abstract
Scheme 1: Representative examples of multisubstituted CF3-alkenes.
Scheme 2: Catalytic synthesis of CF3-alkenes via trifluoromethylation.
Scheme 3: Our strategies for synthesis of CF3-alkenes.
Scheme 4: Synthesis of geminal bis(trifluoromethyl)alkenes.
Scheme 5: A possible reaction mechanism.
Figure 1: Time profile of the photocatalytic trifluoromethylation of 2a with 1a with intermittent irradiation...
Graphical Abstract
Scheme 1: Photohydroxymethylation of carbonyl compounds and imines.
Scheme 2: Model process: photocatalyzed acetophenone/methanol reaction.
Scheme 3: Photocatalyzed acetophenone/methanol reaction: types I–III.
Scheme 4: Photohydroxymethylation and subsequent lactonization of keto esters.
Scheme 5: Model reaction for heterogeneous and dye-sensitized catalysis.
Scheme 6: Product forming routes I to III for photoredox catalysis of methanol/carbonyl compounds.
Scheme 7: Photoredox initiated steps on semiconductor particle surfaces, CB, VB = conduction and valence band....
Graphical Abstract
Figure 1: Representative examples of lamellarin alkaloids.
Scheme 1: Photocatalytic metal free construction of pyrrolo[2,1-a]isoquinolines.
Scheme 2: Evaluation of the substrate scope.
Scheme 3: Evaluation of the substrate scope with activated alkynes.
Graphical Abstract
Figure 1: Selected examples of endoperoxide-containing natural products.
Scheme 1: Endoperoxide formation via cation radicals. In both examples, single electron oxidation is followed...
Scheme 2: Diversification strategy for endoperoxide synthesis by single electron transfer. E*red vs SCE [20].
Figure 2: ORTEP of 3a.
Scheme 3: Proposed mechanism for endoperoxide synthesis from tethered dienes.
Scheme 4: Competing formal [3,3] pathway.
Graphical Abstract
Scheme 1: Strategies for the visible light-catalysed deoxygenation of alcohols (reagents needed in (over-)sto...
Scheme 2: Reduction potentials of investigated derivatives 1–3 in DMF.
Scheme 3: Initial reaction conditions for deoxygenation candidates 1–3.
Scheme 4: Proposed reaction mechanism with and without additional water.
Scheme 5: Calculated spin densities of the radical anion and its protonated species.
Scheme 6: Synthesis of monobenzoate 6e.
Scheme 7: Reduction of benzoate moiety in case of non-benzylic alcohols.
Scheme 8: Optimized conditions for larger scale applications.
Graphical Abstract
Scheme 1: Control experiment with liquid bromine for bromoethrification of alkenols.
Scheme 2: Proposed mechanism for the photocatalytic bromoetherification of alkenols.
Graphical Abstract
Scheme 1: Visible-light-induced sp3 C–H bond functionalization of tertiary amines.
Scheme 2: Substrate scope for aerobic oxidative cyclization of N,N-dimethylanilines with maleimides.
Scheme 3: A proposed reaction mechanism.
Graphical Abstract
Scheme 1: Photooxidation of the substrate and reductive quenching of the photocatalyst (left) vs photoreducti...
Scheme 2: Mechanism of the Markovnikov-type photocatalytic addition of methanol to 1,1-diphenylethylene (1) a...
Scheme 3: Intramolecular photocatalytic addition with substrate 3; reaction conditions: 3 (2 mM), Py (2 mM), ...
Scheme 4: Proposed mechanism of the anti-Markovnikov-type photocatalytic addition of methanol to 1,1-diphenyl...
Figure 1: Conversion of substrate 1 and formation of product 5 observed during photocatalysis with PDI in the...
Figure 2: Conversion of substrate 1 (black dashed) and formation of product 5 (red solid) observed during pho...
Figure 3: Spectra of PDI before (dotted black) and after excitation (red), then every 2 min until ground stat...
Scheme 5: Intramolecular additions of substrates 8 and 10 to demonstrate the effect of different electron den...