Photoredox Catalysis in Radical Addition Reactions

Photoredox catalysis harnesses visible‐light excitation of a photocatalyst to mediate single‐electron transfer events, generating carbon-centred radicals under mild conditions. These radicals undergo addition across unsaturated bonds—most prominently electron-deficient alkenes—enabling rapid construction of C–C linkages with high functional-group tolerance. The generality of this approach spans decarboxylative conjugate additions, Giese-type processes and radical-polar crossover sequences. Key design principles include tuning the excited-state redox potentials of catalysts, selecting appropriate oxidant or reductant quenchers and controlling reaction kinetics to suppress undesired back-electron transfer. As a result, photoredox-enabled radical addition has found broad application in the synthesis of complex natural products, pharmaceutical scaffolds and advanced materials, offering sustainable alternatives to classical radical initiators or harsh thermal conditions.

Research from Nature Portfolio

Recent studies have provided detailed mechanistic insight into decarboxylative radical addition by combining transient absorption spectroscopy with model photoredox systems. Ultrafast measurements of radical lifetimes in a dual photooxidant pair have revealed sub-microsecond kinetics for carboxyl radical formation and decay, pinpointing the lifetimes of key intermediates. This work demonstrates how precise clocking of radical generation and quenching steps can guide the rational design of next-generation photocatalysts, optimise turnover numbers and improve selectivity in radical addition pathways.

Photoredox Catalysis in Radical Addition Reactions publication trend

The graph below shows the total number of articles in photoredox catalysis in radical addition reactions across all publications each year (not limited to Nature Index journals).

Technical terms

Photoredox catalysis: Light-mediated redox activation of a catalyst to shuttle electrons and generate reactive radical intermediates.

Radical addition: A process in which a free radical adds across an unsaturated bond to form a new covalent linkage.

Giese reaction: Radical conjugate addition of carbon-centred radicals to electron-deficient alkenes, named after the pioneering work in 1,4-addition chemistry.

Single-electron transfer (SET): An elementary electron-transfer step by which one electron moves between species, initiating radical formation.

Quenching cycle: The pathway—oxidative or reductive—by which an excited photocatalyst returns to its ground state via electron transfer with a quencher.

References

1. Picosecond to millisecond tracking of a photocatalytic decarboxylation reaction provides direct mechanistic insights. Nature Communications (2019).
2. Direct decarboxylative Giese amidations: photocatalytic vs. metal- and light-free. Chemical Science (2023).
3. Iterative One-Carbon Homologation of Unmodified Carboxylic Acids. Journal of the American Chemical Society (2024).
4. Direct decarboxylative Giese reactions. Chemical Society Reviews (2022).