Photoinduced carbene transfer for copper-catalyzed asymmetric [4 + 1] cycloadditions: an entry to chiral indolines bearing quaternary stereocenters

Abstract

Indoline skeletons are widely found in many natural isolates and pharmaceuticals, making indoline synthesis an ongoing research hotspot in synthetic chemistry. However, the catalytic asymmetric de novo construction of indolines bearing chiral quaternary stereocenters remains challenging. Herein, we present a solution to this unmet challenge through copper-catalyzed asymmetric [4 + 1] cycloadditions of ethynylbenzoxazinones with sulfur ylides, which are formed in situ by photoinduced carbene transfer. As a result, a wide range of chiral indolines bearing C2-quaternary stereocenters are obtained with good enantio- and diastereoselectivities (up to 19 : 1 dr and 96 : 4 er).