LAUSR

Abstract The reaction of N’-(aryl)benzothiohydrazides with 2-chloro-7-cyclopropyl-3-nitro-4-oxothieno[2,3-b]pyridine-5-carboxylic ester/acid in the presence of triethylamine furnished, upon addition of iodomethane, the respective 1,3,4-thiadiazoline-(6-methylthio-4-oxopyridine) hybrids. Interestingly, the reaction of thiohydrazides with 4-oxothieno[2,3-b]pyridines incorporating N1-(2’-halogeno-5’-nitrophenyl) entities generated 1,3-thiazoline ring embedded in the resulting [fused]-tricyclic products. Similarly, the N1-(2’-chloropyridin-3’-yl) analog produced the respective thiazolo[3,2-a: 5,6-b’]dipyridine-thiadiazoline hybrid. Monocyclic 2-chloro-3-nitrothiophenes in their reaction with benzothiohydrazide formed notable thiophene ring-opening products. This behavior is verified by quantum mechanical calculations. The new compounds were characterized by NMR and MS spectral data, and confirmed by X-ray crystallography where feasible. A proposed mechanistic pathway for this new reaction involving preferential predominance of thiophene ring-opening over Smiles rearrangement is presented.