Construction of sulfur stereocentres by asymmetric geminate recasting

Radical pairs generated by light-induced or heat-induced bond cleavage play a central role in biochemical transformations and the synthesis of pharmaceuticals, polymers and industrial chemicals. When such cleavage occurs at a stereocentre in chiral molecules, recombination of the produced radicals can lead to either enantiomer, typically resulting in racemization. Achieving selective conversion of racemic mixtures into single enantiomers is highly desirable yet challenging due to the uncontrolled behaviour of free radicals. Here we show that stereocontrol over these reactions can be achieved through asymmetric geminate recasting: a process in which homolysis and recombination occur within a solvent cage under the influence of a chiral photocatalyst. This strategy enabled the selective construction of chiral sulfur stereocentres via deracemization of sulfinamides, providing access to valuable sulfur-containing building blocks. The approach opens unexplored possibilities for controlling stereochemistry in radical reactions and may inspire broader applications in asymmetric synthesis, medicinal chemistry and materials development.