Photoredox Catalysis in Radical Thiol-Ene Reactions

Photoredox catalysis has emerged as a powerful strategy for effecting radical thiol-ene reactions under mild, sustainable conditions. By harnessing visible light to activate a photocatalyst, electrons are shuttled to generate thiyl radicals that undergo selective addition across carbon–carbon double bonds. This approach offers anti-Markovnikov regioselectivity, high functional-group tolerance and the capacity to operate at ambient temperature without stoichiometric initiators. Mechanistically, the process may proceed via oxidative or reductive quenching cycles in which a photoexcited catalyst transfers an electron to or from the thiol substrate, followed by proton or hydrogen-atom transfer to complete the radical chain. Recent advances have focused on the control of radical generation through tailored photocatalyst design, on the integration of dual catalytic modes to access cascade or multicomponent transformations, and on the development of continuous-flow reactors for scalable operation. Applications extend from the construction of thioether linkages in small-molecule synthesis and late-stage functionalisation of bioactive scaffolds to the fabrication of polymer networks and hydrogels in materials science. Despite rapid progress, challenges remain in expanding enantioselective variants, broadening substrate scope to include electron-poor alkenes and in fine-tuning reaction kinetics to suppress side-chain transfer processes. The global significance of this chemistry lies in its capacity to replace harsh radical initiators with photon-mediated pathways, thereby advancing both green chemistry principles and practical access to C–S bond–containing architectures.

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Photoredox Catalysis in Radical Thiol-Ene Reactions publication trend

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

Technical terms

Photoredox catalysis: Use of light and a photocatalyst to drive redox reactions via electron or energy transfer.

Thiyl radical: Sulfur-centred radical species that add across unsaturated carbon–carbon bonds.

Anti-Markovnikov addition: Regioselective reaction in which the nucleophile adds to the less substituted carbon of an alkene.

Hydrogen atom transfer (HAT): Radical process in which a hydrogen atom is abstracted or donated between species.

Photocatalyst: Molecule or material that absorbs light to initiate chemical transformations without being consumed.

References

1. Recent Advances in Visible-Light Photoredox Catalysis for the Thiol-Ene/Yne Reactions. Molecules (2022).
2. Purple‐Light Promoted Thiol‐ene Reaction of Alkenes. Advanced Synthesis & Catalysis (2023).
3. Intermolecular Photocatalytic Chemo‐, Stereo‐ and Regioselective Thiol–Yne–Ene Coupling Reaction. Angewandte Chemie (2022).