Unprecedented Dual Radical Initiation in Visible-Light Photoredox-Catalyzed X–H (X = Si and B) Insertions of Sulfoxonium Ylides

Unusual chameleonic roles of sulfoxonium ylides, acting as both radical initiators and radical acceptors, are revealed via synergistic experimental and computational studies for the visible-light photoredox-catalyzed Si–H insertion of sulfoxonium ylides with hydrosilanes. Remarkably, when sulfoxonium ylides play the role of radical initiator, an unprecedented dual radical initiation is proposed, in which two radical species, generated in a photoredox catalytic loop via single-electron oxidation and single-electron reduction, respectively, can both trigger H atom transfer processes with hydrosilanes to afford a silyl radical. Subsequently, the yielded silyl radical can attack the C═S moiety of sulfoxonium ylide to fulfill a radical chain mechanistic pathway to furnish the desired product, where sulfoxonium ylides perform as a radical acceptor. This protocol employs easily accessible reagents and demonstrates a wide substrate scope with satisfied yields under benign conditions. Additionally, the construction of C–B bonds via analogous visible-light photoredox-catalyzed B–H insertion of sulfoxonium ylides with amine boranes is also realized.