DBU-catalysed cascade nucleophilic addition/cyclization to access 7-nitro (ester) imidazo[1,2-a] pyridin-8-amines

Abstract

In this report, we present the first examples of DBU-catalysed cascade reactions involving 1-(3-alkynyl)-1H-imidazole-2-carbonitriles and CH-acids such as nitromethane and malonates. This solvent-free transformation occurs through the nucleophilic CH-acid addition to the carbonitrile, leading to the formation of a push–pull enamine, which is subsequently followed by intramolecular cyclization. As a result, two new C–C bonds were created in a single step with remarkable regioselectivity. This approach provided unprecedented direct access to C-7 nitro, C-8 amine and C-7 ester, C-8 amine-substituted imidazo[1,2-a] pyridines, which serve as valuable scaffolds that were previously unattainable.