4-Oxo-1-phenyl-4,7-dihydropyrazolo[3,4-b]pyridine-5-carbonitrile compound (4) was prepared by the
reaction of 5-amino-3-methyl-1-phenyl pyrazole (1) with ethyl 2-cyano-3-ethoxyacrylate followed by
cyclization using diphenyl ether. The pyrazolopyridinone compound 4 was converted to the
chloropyrazolopyridine 5 by the reaction with phosphorus oxychloride. Compound 5 was used as a starting
material to synthesize 3-amino-4-substituted pyrazolothienopyridine derivatives 10a–f and ethyl-3-
aminopyrazolopyrrolopyridine-2-carboxylate 21, which were used as a versatile precursors for synthesis
of poly-fused heterocyclic compounds.