A new synthesis of substituted imidazo[4,5-b]pyridinones by reductive cyclisation of 4-nitro-1H-imidazol-5-yl di- and tri-carbonyl compounds

A new synthetic route to the biologically important imidazo[4,5-b]pyridine ring system is described. An efficient method for the condensation of 4-nit ro-1H-imidazole-5-carbonyl chlorides with activated methylene compounds usi ng magnesium ethoxide has been developed. The imidazolyl di- and tri-carbon yl compounds formed in this process were found to be good substrates for re ductive cyclisation to the little studied 4-hydroxyimidazo[4,5-b]pyridinone s by either catalytic hydrogenation over palladium or by treatment with alk aline sodium borohydride in the presence of palladium. Highly oxygenated de rivatives of 1-deazapurines are thus readily available by this method.