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

Abstract

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-nitro-1H-imidazole-5-carbonyl chlorides with activated methylene compounds using magnesium ethoxide has been developed. The imidazolyl di- and tri-carbonyl compounds formed in this process were found to be good substrates for reductive cyclisation to the little studied 4-hydroxyimidazo[4,5-b]pyridinones by either catalytic hydrogenation over palladium or by treatment with alkaline sodium borohydride in the presence of palladium. Highly oxygenated derivatives of 1-deazapurines are thus readily available by this method.