New and Efficient Synthesis oflmidazo[4,5-b]pyridine-5-ones

l-Aryl-5-amino-4-cyanoformimidoylimidazoles 1 were reacted with methyl cyanoacetate, under mild experimental conditions, leading to 3-aryl-6,7-dicyanoimidazo[4,5-b]pyridine-5-ones 5, isolated after neutralization of their ammonium salts 4. A reaction intermediate, imidazole 3d, the precursor of the bicyclic structure 5d, could be isolated under carefully controlled experimental conditions and was shown to cyclize to imidazo[4,5-b]pyridine-5-one (4d, isolated as the DBU salt) after reflux in ethanol, in the presence of DBU.