Electrochemically enabled dearomative [2 + 2] cycloadditions of indoles with alkynes to access cyclobutene-fused indolines

Abstract

A general protocol for regioselective electrochemical [2 + 2] cyclization of N-acyl indoles with alkynes was described. This novel method was carried out under mild, chemical oxidant-free, and transition-metal-free conditions, with a broad substrate scope and good functional group tolerance to provide cyclobutene-fused indolines with high regioisomeric ratios and was readily scalable to the gram scale. Mechanistic studies have suggested that the selective reduction of radical cations at the cathode to form a double radical intermediate is the key step in the reaction.