Enantioselective organocatalytic radical alkylation enabled by photoexcitation

Abstract

Photoinduced single-electron transfer generates radicals that could engage in radical–radical cross-coupling reactions, but organocatalytic photocatalyst-free systems for enantioselective processes remain rare and challenging. Herein, we report a light-driven enantioselective alkylation of 3-hydroxyoxindoles with NHPI esters, providing a new route for a variety of 3-alkyl-3-hydroxy oxindole derivatives. The reaction follows a light-driven electron transfer/radical cross-coupling process by using a readily available chiral guanidine organocatalyst and PPh₃ without additional photocatalysts. The mechanistic studies reveal that the guanidine catalyst and phosphine benefit the formation of an excited enol reductant and an NHPI oxidant for electron transfer, respectively, and the chiral bifunctional catalyst also provides an H-bond network to guide outer-sphere radical coupling in an enantioselective manner.