Visible-Light-Driven Photocatalytic Activation of Inert Sulfur Ylides for 3-Acyl Oxindole Synthesis

Bicarbonyl‐substituted sulfur ylide is a useful, but inert reagent in organic synthesis. Usually, harsh reaction conditions are required for its transformation. For the first time, it was demonstrated that a new, visible‐light photoredox catalytic annulation of sulfur ylides under extremely mild conditions, permits the synthesis of oxindole derivatives in high selectivities and efficiencies. The key to its success is the photocatalytic single‐electron‐transfer (SET) oxidation of the inert amide and acyl‐stabilized sulfur ylides to reactive radical cations, which easily proceeds with intramolecular C−H functionalization to give the final products. Visible‐light photocatalytic, single‐electron‐transfer oxidations of inert sulfur ylides generate active radical cations, which enable subsequent intramolecular C−H functionalization to provide significant 3‐acyl oxindoles (see scheme). This result is the first example of photochemical annulations of dicarbonyl‐stabilized sulfur ylides under extremely mild reaction conditions.