Thiophene ring-opening reactions VI. Attempted cyclization towards [fused]-tricyclic system involving a thiolate anion and suitably located electrophilic carbon

Abstract

Model α-chloro-β-nitrothieno[2,3-c]pyridazines incorporating N1-(aryl) entity appended with ortho-methoxycarbonyl or trifluoromethyl group were prepared via intramolecular cyclization of their respective N-arylhydrazone precursors. Interaction of these substrates with N'-(p-fluorophenyl)benzothiohydrazide, in the presence of NEt₃, furnished the respective 1,3,4-thiadiazoline-pyridazine thiolate hybrids that were S-methylated to produce the corresponding "sulfanyl" derivatives. Their structures were deduced from spectral data, and confirmed by single-crystal X-ray diffraction.

Keywords: N′-(aryl)benzothiohydrazide; formal [4+1] annulation; selective S-methylation; unfavorable cyclization.