Oxidation of thioamides with the DMSO–HCl system: a convenient and efficient method for the synthesis of 1,2,4-thiadiazoles, isothiazolo-[5,4-b]pyridines, and heterocyclic disulfides

Abstract

Brief heating of 3-aryl-2-cyanothioacrylamides in the DMSO–HCl system gave (2E,2′E)-2,2′-(1,2,4-thia-diazol-3,5-diyl)bis(3-arylacrylonitriles). Under the same conditions, cyclic thioamides (derivatives of 2-thioxo-1,2-dihydropyridine-3-carbonitrile and quinoxaline-2(1H)-thione) gave good yields of the bis(hetaryl) disulfides. Ethyl 4-(4-chlorophenyl)-5-cyano-2-phenyl-6-thioxo-1,4,5,6-tetra-hydropyridine-3-carboxylate gave a mixture of oxidation products at the sulfur atom and the hetero-cycle when treated with the DMSO–HCl system. Oxidation of N-aryl-4,6-dimethyl-2-thioxo-1,2-di-hydropyridine-3-carboxamides gave isothiazolo[5,4-b]pyridines.