Efficient One-Step Synthesis of Substituted-pyrazolo[3,4-b]pyridine from Substituted-3-cyano-2(1H)-pyridone

An efficient one-step conversion of 4-phenyl-5-ethoxycarbonyl-3-cyano-6-metlyl-2(1H)-pyridone (1) into ethyl 3-amino-6-methyl-4-phenyl-1H-pyrazolo[3,4-b]pyridine-5-carboxylate (7) is described. An unusual hydrazine mediated decarboxylation of 7 into 3-amino-6-methyl-4-phenyl-1H-pyrazolo[3,4-b]pyridine (8) is reported. The structure of 8 was confirmed by spectral and chemical investigations. A plausible reaction mechanism for the formation of the unexpected product 8 is proposed.