Synthesis of Imidazo[1,2-a]Indoles from 2-Chloroindole-3-Carbaldehyde

Abstract

A two-step approach towards the synthesis of imidazo[1,2-a]indoles from 2-chloroindole-3-carbaldehyde has been developed. It comprises the N-alkylation of indole ring by 2-bromo-1,1-diethoxyethane followed by a treatment with aromatic amine hydrochlorides. The reaction proceeds as a nucleophilic substitution of the chlorine atom at position 2 of the indole ring followed by cyclization along with the condensation at the aldehyde group. Imidazo[1,2-a]indoles were isolated as protonated Schiff bases. Their structure was proved by 1 H and 13 C NMR spectroscopy and X-ray structural analysis.