Abstract: 2-(5-oxothiazolidinone)-cyanoacetamido derivative 3 was prepared in two steps by reaction of 2-(2-cyano-acetylamino)-4,5,6,7-tetrahydro-benzo[b]thiophene-3-carboxamide (1) with phenyl isothiocyanate and chloroacetyl chloride, which diazocoupled with p-tolyldiazonium chloride in pyridine to afford the corresponding hydrazono derivative 4. Also, condensation of 3 with p-anisaldehyde gave the corresponding arylidine derivative 5. Treatment of 2 with dimethyl sulfate afforded the ketene N,S-acetal 9 which give 5-amino pyrazole derivative 10 upon treatment with hydrazine hydrate. Compound 10 was used as key intermediate for synthesis of pyrazolo[5,1-c][1,2,4]triazine 13a, b, pyrazolo[5,1-a]pyrimidine 14–17 and pyrolo pyrazole 18 derivatives. Finally, condensation of 1 with DMF-DMA afforded the corresponding acryloamide derivative 19, which afforded the corresponding pyrazole derivative 20 upon heating with hydrazine hydrate. All new synthesized compounds were evaluated as antimicrobial agents; some of them exhibited promising activities. [Copyright &y& Elsevier]