Brønsted Acid Catalyzed (4 + 2) Cyclocondensation of 3-Substituted Indoles with Donor–Acceptor Cyclopropanes

Abstract

Acylcyclopropanes are employed as useful donor−acceptor cyclopropanes that undergo formal (4 + 2) cyclo-condensation with N-unprotected 3-substituted indoles in thepresence of a Brønsted acid catalyst. The reaction involves thesimultaneous alkylation of both the N and C-2 positions of theindole and provides access to the 8,9-dihydropyrido[1,2-a]indolescaffold that is the central core of several biologically relevantindole alkaloids in excellent yields and good selectivities