Metal-free C–N bond formations: one-pot synthesis of pyrido[2′,1′:2,3]imidazo[4,5-c]cinnolines, benzo[4′,5']thiazolo- and thiazolo[2′,3′:2,3]imidazo[4,5-c]cinnolines

Abstract

An efficient one-pot synthesis of novel pyrido[2′,1′:2,3]imidazo[4,5-c]cinnoline derivatives has been achieved with moderate to good yields, with two C–N bond formations through C–H functionalization of 2-arylimidazo[1,2-a]pyridines. The reaction proceeds via C-3 regioselective hydrazination with diisopropyl azodicarboxylate followed by oxidative N-arylation mediated by phenyliodine(III) diacetate (PIDA) in trifluoroacetic acid by means of C–H functionalization to produce pyrido[2′,1′:2,3]imidazo[4,5-c]cinnolines. Other imidazoheterocycles such as 2-arylbenzo[d]imidazo[2,1-b]thiazoles, and 6-arylimidazo[2,1-b]thiazoles underwent similar transformations giving the corresponding cinnolines under transition metal-free and mild conditions.