Acyl Azolium-Photoredox-Enabled Synthesis of beta-Keto Sulfides

alpha-Heteroatom functionalization is a key strategyfor C-Cbond formation in organic synthesis, as exemplified by the additionof a nucleophile to electrophilic functional groups, such as iminiumions; oxocarbenium ions; and their sulfur analogues, sulfenium ions.We envisioned a photoredox-enabled radical Pummerer-type reactionrealized through the single-electron oxidation of a sulfide. Followingthis oxidative event, alpha-deprotonation would afford alpha-thioradicals that participate in radical-radical coupling reactionswith azolium-bound ketyl radicals, thereby accessing a commonly proposedmechanistic intermediate of the radical-radical coupling enroute to functionalized additive Pummerer products. This system providesa complementary synthetic approach to highly functionalized sulfurousproducts, including modification of methionine residues in peptides,and beckons further exploration in C-C bond formations previouslylimited in the standard two-electron process.