Enaminones as building blocks in heterocyclic preparations: Synthesis of novel pyrazoles, pyrazolo-[3,4-d]pyridazines, pyrazolo[1,5-a]pyrimidines, pyrido[2,3-d]pyrimidines linked to imidazo[2,1-b]thiazole system

Abstract

The unreported 2-[E-3-(N,N-dimethylamino)acryloyl]-3-methyl-5,6- diphenylimidazo[2,1-b]thiazole 3 was prepared via the reaction of 2-acetyl-3- methyl-5,6-diphenylimidazo[2,1-b]thiazole 2 with dimethylformamide dimethyl acetal (DMF-DMA). Enaminone 3 underwent regioselective 1,3-dipolar cycloaddition with nitrilimines 5a-f, to afford the corresponding pyrazoles 7a-f. The reaction of 7a,d,g with hydrazine hydrate, afforded the pyrazolo[3,4- d]pyridazines 8a-c, respectively. Enaminone 3 also reacted with a hydrazines, hydroxylamine hydrochloride, 5-aminopyrazole 11, 6-aminothiouracil 15 and hippuric acid 22. The structures of the newly synthesized compounds were confirmed by spectral data and elemental analyses. © 2012 The Japan Institute of Heterocyclic Chemistry.