New 5-aminopyrazoles 2a-c were prepared in high yields from the reaction of known α,α-dicyanoketene-N,S-acetals 1a-c with hydrazine hydrate under reflux in ethanol. These compounds were utilized as intermediates to synthesize pyrazolo[1,5-a]-pyrimidines 3a-c, 4a-d, 5a-c, and 6a-c, as well as pyrazolo[5,1-c][1,2,4]triazines 7a-c and 8a-c, by the reaction of 2-[bis(methylthio)methylene]malononitrile, α,α-dicyanoketene-N,S-acetals 1a-b, acetylacetone, acetoacetanilide as well as acetylacetone, and malononitrile, respectively. Furthermore, cyclization of 2a-c with pentan-2,5-dione yielded the corresponding 5-pyrrolylpyrazoles 9a-c. Moreover, fusion of 2a-c with acetic anhydride resulted in the corresponding 1-acetyl-1H-pyrazoles 10a-c. The antibacterial activity and cytotoxicity against Vero cells of several selected compounds are also reported.