New 5-aminopyrazoles2aec were prepared in high yields from the reaction of knowna,a-dicyanoke-tene-N,S-acetals1aec with hydrazine hydrate under reflux in ethanol. These compounds were utilized as intermediates to synthesize pyrazolo[1,5-a]-pyrimidines3aec,4aed,5aec, and6aec, as well as pyrazolo[5,1-c][1,2,4]triazines7aecand8aec, by the reaction of 2-[bis(methylthio)methylene]malononitrile,a,a-dicyanoketene-N,S-acetals1aeb, acetylacetone, acetoacetanilide as well as acetylacetone, and malono-nitrile, respectively. Furthermore, cyclization of 2aec with pentan-2,5-dione yielded the corresponding 5-pyrrolylpyrazoles9aec. Moreover, fusion of 2aec with acetic anhydride resulted in the corresponding1-acetyl-1H-pyrazoles10aec. The antibacterial activity and cytotoxicity against Vero cells of several selected compounds are also reported.