Synthesis of a new imidazo[4,5-b]pyridin-5-one via a vicarious nucleophilic substitution of hydrogen

A new imidazo[4,5-b]pyridin-5-one was prepared in five steps from 4(5)-nitro-1H-imidazole via a vicarious nucleophilic substitution of hydrogen of 1-benzyl-4-nitro-1H-imidazole with the carbanion generated from chloroformand potassium tert-butoxide. Hydrolysis of 1-benzyl-5-dichloromethyl-4-nitro-1H-imidazole and Knoevenagel condensation between the resulting aldehyde and diethyl malonate catalyzed by titanium(1V) chloride gave the corresponding 4-nitroimidazole bearing at 4 position the diethyl methylenemalonate group. Reduction and cyclization afforded the required ethyl 1-benzyl-5-oxo-4,5-dihydro-1H-imidazo[4,5-b]pyridine-6-carboxylate.