Base-catalyzed and DMSO-promoted intramolecular hydroalkoxylation to prepare pentacyclic chromeno[4,3-b]indolines

Abstract

A base-catalyzed and DMSO-promoted atom economic intramolecular hydroalkoxylation was developed to prepare a variety of pentacyclic chromeno[4,3-b]indolines in good yields with high regioselectivity and diastereoselectivity. Mechanistic studies revealed that DMSO played important roles as a green solvent and an activator of unactivated alkenes via hydrogen-bonding and ion pairing to facilitate a 5-exo-trig cyclization. The present method highlights mild reaction conditions, short reaction time, broad substrate scope, a new application of DMSO, and gram-scalable preparation without column chromatography.