Photoredox dearomative β-hydroborylation of indoles for the synthesis of borylated indolines

Abstract

A photocatalysed dearomative β-hydroborylation reaction of indole derivatives with NHC-boranes has been accomplished. This protocol shows a broad substrate scope with moderate to excellent yields, providing a novel and efficient route for the preparation of C2- and C3-borylated indolines, which are important structural units in pharmaceuticals, natural products and functional materials. Control experiments elucidated a radical process initiated by photoinduced energy transfer and single-electron transfer for this transformation. Furthermore, gram-scale reactions demonstrated the synthetic value of this method.