A Facile Synthesis of Pyrido[2′,3′:3,4] pyrazolo[1,5-a] pyrimidine and Pyrido[2′,3′:3,4] pyrazolo[5,1-c][1,2,4] triazine Bearing a Thiophene Moiety

Pyridinone derivative 8 was synthesized and transformed into the respective chloropyridine 9, which was allowed to react with hydrazine hydrate to afford pyrazolo[3,4-b] pyridin-3-amine derivative 11. Compound 11 was used as a key intermediate for a facile synthesis of the title compounds 14, 15, 17, 21a, b, and 24a-c where the reaction of 11 with some 1,3-dielecrophiles resulted in the formation of pyrido[2',3' : 3,4] pyrazolo[1,5-a] pyrimidines 14, 15, and 17, whereas diazotization of compound 11 gave the respective diazonium salt 18 which was coupled with some active methylene-containing compounds to give the corresponding hydrazones 19a, b and 22a-c. Cyclization of the latter hydrazones yielded the pyrido[2',3' : 3,4] pyrazolo[5,1-c][1,2,4] triazines 21a, b and 24a-c, respectively.