Decoupling Radical Trapping from Stereochemical Control: Dual Incorporation of CF 2 H and SO 2 into Allenes via a Photoredox-Catalyzed Curtin–Hammett Scenario

The radical addition to SO 2 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 SO 2 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 SO 2 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 S N Ar 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.