Enantioselective Oxidative Enolate Coupling of Oxindoles Catalyzed by Chiral Guanidinium Hypoiodite

Hypoiodite is an environmentally friendly oxidant that has been developed to drive a variety of bond-forming reactions. Recently, asymmetric oxidative bond-forming reactions using hypoiodite in the presence of chiral onium organocatalysts have been used to synthesize carbon–heteroatom bonds, but asymmetric carbon–carbon bond-forming reactions have not been reported. Herein, we present an oxidative enolate coupling reaction of oxindoles to provide optically active oxindole dimers bearing consecutive all-carbon quaternary stereogenic centers, using a chiral guanidinium hypoiodite catalyst. This reaction affords the corresponding homocoupling products with high enantioselectivity. We also describe oxidative enolate cross-coupling reactions of two oxindoles bearing electronically distinct substituents.