Carbon-nitrogen bond formation in cyclisations by deoxygenation, thermolysis, or photolysis of phenylimidazo[1,2-a]pyridine systems: access to pyrido[1′,2′ : 1,2]imidazo[4,5-b]indoles

Reductive cyclisation of 2-(2-nitrophenyl)imidazo[1,2-a]pyridine with triethyl phosphite gives the indolic structures (5) and (6). The latter are of interest because of preferential C insertion rather than reaction of the nitrene at N-1 of the imidazole ring. 2D N.m.r. confirms structure (5). Both thermolysis or photolysis of the representative 2-(2-azidophenyl)imidazo[1,2-a]pyridines (7) and (8) are also reported and shown to produce novel indole, cinnoline, and benzofuran structures in an extremely facile fashion.