Photoredox-Catalyzed Reductive Coupling of Organic Molecules

Photoredox-catalyzed reductive coupling employs visible light and photocatalysts—often transition-metal complexes or organic dyes—to drive single-electron transfer events that generate carbon-centred radicals, radical anions or carbanion equivalents. By inverting the native polarity of substrates (umpolung) such as alkenes, imines and carbonyls, these methods enable direct C–C bond formation under mild conditions without stoichiometric organometallic reagents. A typical sequence involves photoexcitation of the catalyst, one-electron reduction of a substrate to form a reactive radical intermediate, addition to an electrophile and subsequent reduction or proton-coupled electron transfer to furnish a coupled product. Developments in multi-photon excitation and dual catalysis have expanded the scope to include sequential carbanion generation from sp3-hybridised alkenes, ketyl radical formation from carbonyls and convergent multicomponent assemblies. These approaches offer sustainable access to diverse scaffolds—alcohols, amines and amino acids—with precise control over regio-, diastereo- and enantioselectivity, streamlining the synthesis of complex bioactive molecules.

Research from Nature Portfolio

Recent studies have introduced multi-photon excitation strategies to generate alkyl carbanion equivalents from aryl alkenes, enabling sequential C–C bond formation with carbonyl electrophiles to afford hydroalkoxylation, hydroamidation, aminoalkylation and carboxyaminoalkylation products under mild visible-light irradiation. Central to this approach is the controlled formation of a distonic radical anion that undergoes nucleophilic addition followed by a reductive polar crossover to produce a second carbanion. Foundational work has also demonstrated dual catalysis merging photoredox and Lewis acid activation to enable enantioselective convergent coupling of nitrone substrates with aromatic ketyl radicals. This strategy exploits a radical-type Zimmerman–Traxler transition state and chiral ligands to achieve high enantio- and diastereoselectivities in the synthesis of vicinal amino alcohols, showcasing photoredox-enabled stereocontrol in reductive coupling.

Photoredox-Catalyzed Reductive Coupling of Organic Molecules publication trend

The graph below shows the total number of articles in photoredox-catalyzed reductive coupling of organic molecules across all publications each year (not limited to Nature Index journals).

Technical terms

Photoredox catalysis: use of light-activated catalysts to mediate single-electron transfer events.

Radical anion: a negatively charged radical species formed by one-electron reduction of a neutral molecule.

Carbanion: a carbon-centred anion acting as a nucleophile in bond-forming reactions.

Ketyl radical: a radical anion generated by single-electron reduction of a carbonyl group.

Umpolung: inversion of the normal reactivity polarity of a functional group to enable unconventional bond formation.

References

1. Photocatalytic generation of alkyl carbanions from aryl alkenes. Nature Catalysis (2024).
2. Acridine photocatalysis enables tricomponent direct decarboxylative amine construction. Chemical Science (2024).
3. Dual catalysis for enantioselective convergent synthesis of enantiopure vicinal amino alcohols. Nature Communications (2018).
4. Catalytic Generation and Use of Ketyl Radical from Unactivated Aliphatic Carbonyl Compounds. Organic Letters (2019).
5. Catalytic defluorinative ketyl–olefin coupling by halogen-atom transfer. Chemical Science (2022).