Heterocyclic synthesis via enaminones: Regioselective synthesis of some novel pyrazole, isoxazole, pyrimidine, pyrido[1,2-a]benzimidazole and pyrazolo[1,5-a]-pyrimidine derivatives

2-Acetylbenzothiazole (1) reacts with dimethylformamide dimethylacetal (DMF-DMA) to afford the enaminone 2. Compound 2 reacts regioselectively with some nitrilimines 5a–d and nitrile oxides 6b–d to afford the novel pyrazole and isoxazole derivatives 11a–d and 12b–d, respectively, which react with hydrazine hydrate to give the new pyrazolo[3,4-d]pyridazine and isoxazolo[3,4-d]pyridazine derivatives 13a–d and 14b–d, respectively. The enaminone 2 reacts with 1H-benzimidazole-2-acetonitrile (17) to afford the pyrido[1,2-a]benzimidazole derivatives 19. Compound 2 reacts also with 5-amino-3-phenylpyrazole (20) and with guanidine to afford the new pyrazolo[1,5-a]pyrimidine and the 2-aminopyrimidine derivatives 22 and 24, respectively.