Brønsted acid catalyzed multicomponent synthesis of N-arylindole and N-arylbenzo[e]indole

Abstract

The indole skeleton was efficiently constructed via a practical acid-catalyzed multicomponent reaction (MCR) using readily accessible anilines, 4-hydroxycyclohexanone or 2-tetralone, and 2,2-dimethoxyacetaldehyde. This transformation proceeds through a cascade pathway involving aldol condensation, deprotonative aromatization and intramolecular cyclization. As a facile acid-mediated annulative MCR protocol, this method enables the convenient synthesis of C2,C3-unsubstituted indoles under mild and environmentally benign reaction conditions. The scope of the reactions was scouted and more than 40 derivatives were described.