Synthesis of hydroindoles via desymmetric [3+2] cycloadditions of para-quinamines with photogenerated ketenes

Abstract

A DBU-catalyzed desymmetric [3+2] cycloaddition between para-quinamines and photogenerated ketenes was developed for the first time. Under the irradiation of low-energy blue LEDs, a variety of hydroindoles bearing all-carbon quaternary centers were produced with good reaction efficiency and complete diastereoselectivity (34 examples, 45–99% yields and >95 : 5 dr). This protocol represents a new approach to synthetically significant hydroindoles, and features broad substrate scope, high functional group compatibility and mild reaction conditions.