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. (C) 1999 John Wiley & Sons, Inc.