Pyrazolo[3,4-b]pyridine in heterocyclic synthesis:: synthesis of new pyrazolo[3,4-b]pyridines, imidazo[1′,2′:1,5]pyrazolo[3,4-b]pyridines, and pyrido[2′,3′:3,4]pyrazolo[1,5-a]pyrimidines

Pyrazolo[3,4-b]pyridine derivatives 7 and 9 were synthesized via the reaction of 3-amino-1H-pyrazolo- [3,4b-]pyridine derivative 2 with omega bromoacetophenones. Reaction of 7 and 9 with Ac2O afforded the imidazo[1',2':1,5]pyrazolo[3,4-b]pyridine derivative 8 and pyrazolo[3,4-b]pyridine derivative 10, respectively. Reaction of 2 with chloroacetonitrile followed by DMF-DMA gave imidazo[1',2':1,5]pyrazolo[3,4-b]pyridines 4 and 5, respectively. Acetylacetone and 1,1-dicyano-2,2-dimethylthioethene were reacted with 2 to afford the pyrido[2',3':3,4]pyrazolo-[1,5-a]-pyrimidines 11 and 14, respectively. Also, 2 reacted with DMF-DMA to yield the formamidine 15, which in turn, reacted with active methylene reagents, yielding the corresponding pyrido[2',3':3,4]pyrazolo[1,5-a]pyrimidines 18 and 23a-23d.