Annulation of imidazo[1,2-a]pyridines under metal-free conditions

Abstract

A base promoted protocol for the synthesis of benzo[a]imidazo[5,1,2-cd]indolizines from 2-arylimidazo[1,2-a]pyridines and benzyne precursors under metal-free conditions has been developed. Without a transition metal, double C(sp²)–H activation of 2-phenylimidazo[1,2-a]pyridines under basic conditions was achieved. This method is also applicable for the annulation of imidazo[1,2-a]pyrimidine and naphthylamine under the same conditions. These annulated molecules showed fluorescence characteristics and hence their photo physical properties were evaluated.