The radical addition to SO2 represents a powerful strategy for the synthesis of sulfone compounds. Allylic radicals are highly reactive transient species, and achieving stereoselective radical coupling between 1,1-disubstituted allylic radicals and SO2 has remained a significant challenge. Here, we overcome the inherent limitations–low reaction barriers and thermodynamic reversibility─in the stereocontrol of allylic radical addition to SO2 by establishing a light-driven dynamic equilibrium, enabling the highly E/Z-selective 1,2-difluoromethylation/polyfluoroarylsulfonylation of allenes. Key to this process is the light-mediated oscillation between sulfonyl radicals and sulfinate anions, which facilitates a modified Curtin–Hammett scenario to decouple the radical C–S bond formation from the stereodetermining step. Stereocontrol is ultimately achieved in the rate-determining SNAr step. Our conclusions are supported by detailed DFT calculations and mechanistic experiments. The fundamental concept of leveraging photoredox-catalyzed reversible equilibria to decouple radical bond formation from stereochemical determination offers a general blueprint for addressing long-standing challenges in stereoselective radical reactions.
Guo et al. (Wed,) studied this question.