Photocatalytic Reductive Radical‐Polar Crossover for a Base‐Free Corey–Seebach Reaction

A metal‐free generation of carbanion nucleophiles is of prime importance in organic synthesis. Herein we report a photocatalytic approach to the Corey–Seebach reaction. The presented method operates under mild redox‐neutral and base‐free conditions giving the desired product with high functional group tolerance. The reaction is enabled by the combination of photo‐ and hydrogen atom transfer (HAT) catalysis. This catalytic merger allows a C−H to carbanion activation by the ion of a hydrogen atom followed by radical reduction. The generated nucleophilic intermediate is then capable of adding to carbonyl electrophiles. The obtained dithiane can be easily converted to the valuable α‐hydroxy carbonyl in a subsequent step. The proposed reaction mechanism is supported by emission quenching, radical–radical homocoupling and deuterium labeling studies as well as by calculated redox‐potentials and bond strengths. Picture perfect: A photocatalytic approach for the Corey–Seebach reaction is presented. This base‐ and metal‐free reaction exploits the combination of photo‐ and HAT‐catalysis furnishing the desired product under mild conditions with a high functional group tolerance. The reactive intermediate is generated by hydrogen atom ion followed by radical reduction rendering a carbanion nucleophile capable of adding to aldehydes and ketones.