Photocatalytic intermolecular [2+2] cycloaddition/dearomatization of indoles: easy access to cyclobutane-fused indolines

Abstract

Visible-light-promoted [2+2] cycloaddition/dearomatization of aromatic compounds is an efficient strategy for the synthesis of three-dimensional rigid four-membered ring to realize the modification of organic molecules, which boasts great potential and prospect in developing first class drugs. Herein, cyclobutane-fused indolines were successfully synthesized via photocatalytic intermolecular [2+2] cycloaddition/dearomatization reaction with olefins. This reaction exhibited excellent regio- and stereoselectivity (> 20:1 dr), high atom- and step-economy, and was characterized by mild and green reaction conditions, simple operation, wide range of substrate applicability. The mechanistic control exploration suggested that the [2+2] cycloaddition reaction was initiated by the triplet-triplet energy transfer paradigm.