Accessing Allylic Sulfones from Allyl Bromides via SO₂ Insertion under Dual Photoredox/Lewis Base Catalysis

Herein, we report a transition-metal-free, dual photoredox/Lewis base-catalyzed method for synthesizing allylic sulfones from allyl bromides via SO₂ insertion. The reaction mechanism involves a radical-radical coupling pathway, while the allylic radical is generated from an ammonium cation via a SET process. Mechanistic studies demonstrate the existence of both allylic and sulfonyl radical intermediates. Notably, this general and efficient strategy affords allylic sulfones containing coumarin, cinnamonitrile, or cinnamic ester groups with high regioselectivity, showcasing broad substrate scope.