Cobalt Metallaphotoredox Catalysis Enabled Three‐Component Radical Allylic Sulfonylation via C–H Functionalization ^†

Comprehensive Summary Allylic sulfones represent important structural motifs frequently found in bioactive molecules and serve as versatile synthetic intermediates. Consequently, the development of efficient synthetic routes to these valuable scaffolds remains a significant and ongoing pursuit in chemistry. Conventional synthetic methods often rely on noble‐metal catalysts or pre‐functionalized substrates and are predominantly limited to the formation of allylic aryl sulfones. Recently, multicomponent sulfonylation strategy involving sulfur dioxide insertion has emerged as an attractive alternative. However, existing approaches within this paradigm generally still require pre‐functionalized alkene substrates, and general examples of multicomponent sulfonylation reactions that employ readily available alkenes via SO 2 insertion to afford allylic alkyl sulfones remain scarce. Herein, we report an earth‐abundant cobalt metallaphotoredox catalyzed three‐component allylic C–H sulfonylation reaction that enables direct and complementary access to allylic alkyl sulfones. This method employs readily available alkenes, DABSO as a sulfur dioxide surrogate, and cyclobutanone oxime esters as radical precursors. Mechanistic investigations reveal that the cobaloxime catalyst plays a dual role, combining photoredox and hydrogen atom transfer (HAT) capabilities, which is critical for driving the transformation. This approach operates without noble‐metal catalyst and pre‐functionalization, and exhibits operational simplicity, broad functional group tolerance, and high chemo‐ and regioselectivity. The utility of this methodology is demonstrated through scalable synthesis and late‐stage functionalization of pharmaceutical derivatives. This protocol thus provides a novel and complementary route for the direct synthesis of allylic alkyl sulfones from unfunctionalized alkenes.