Syntheses of some new azolopyrido‐[4′,3′:4,5]thieno[2,3‐d]pyrimidines

Diethyl 2‐(ethoxythioxomethyl)amino]‐4,5,6,7‐tetrahydrothieno2,3‐c]‐pyridine‐3,6‐dicarboxylate 2 , prepared from diethyl 2‐isothiocyanato‐4,5,6,7‐tetrahydrothieno2,3‐c]pyridine‐3,6‐dicarboxylate 1 by boiling in anhydrous ethanol, was converted into pyrido4′,3′:4,5]thieno2,3‐d]pyrimidine derivatives 3, 4 by treatment with hydrazine hydrate. The tetracyclic systems imidazo1,2‐a]pyrido‐4′,3′:4,5]thieno2,3‐d]pyrimidine 9 and pyrido4′,3′:4,5]thieno2,3‐d]1,3]thiazolo‐3,2‐a]pyrimidine 10 were synthesized by the reaction of 2 with 1,2‐diaminoethane and aminoethanethiol, respectively. The hydrazino derivative 4 underwent cyclization reactions with orthoesters and nitrous acid to give the corresponding pyrido4′,3′:4,5]thieno2,3‐d]1,2,4]triazolo1,5‐a]pyrimidines 5, 6 and pyrido4′,3′:4,5]thieno3,2‐e]1,2,3,4]tetrazolo1,5‐a]pyrimidine 8 , respectively. Moreover, reactions of 3 with cyanogen bromide, N‐carbethoxyhydrazine, carbon disulfide, and ethylchloroformate resulted in the formation of the new pyrido4′,3′:4,5]thieno2,3‐d]1,3,4]thiadiazolo3,2‐a]pyrimidine derivatives 12–15 . © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:280–286, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10030