Synthesis of annelated 1,3,4,6-thiatriazepines from reaction of cyclic thioureas with 1,4-dichloro-2,3-diazabutadienes

Abstract

Acyclic thioureas react with 1,4-dichloro-1,4-diphenyl-2,3-diazabutadiene in the presence of triethylamine or sodium hydride to give mainly 2,5-diphenyl-1,3,4-thiadiazole. By contrast, the cyclic thioureas imidazoline-2-thione, dihydropyrimidine-2-thione, 4-oxopyrimidine-2-thione, 6-methyl-4-oxopyrimidine-2-thione, and benzimidazole-2-thiol, react with 1,4-dichloro-1,4-diphenyl-2,3-diazabutadiene, and, in the case of imidazoline-2-thione, also with 1,4-dichloro-1,4-bis(4-chlorophenyl)-2,3-diazabutadiene, in the presence of a two-molar proportion of sodium hydride, to give the series of 2,5-diphenyl-[1,2-f]-1,3,4,6-thiatriazepines: (7a)(35%), (7b)(63%), (9a)(36%), (9b)(26%), (8)(49%), and (7c)(29%), respectively. Formation of the thiatriazepines is accompanied by variable amounts of 2,5-diaryl-1,3,4-thiadiazoles (2a,b). Acid hydrolysis of the diarylthiatriazepines yields a mixture of breakdown products, of which the principal components are the diphenylthiadiazole (2a)(12–90%), 2,5-diphenyl-1,3,4-oxadiazole [12% from compound (7b)], the corresponding thione (21–22%), and, from the thiatriazepinones (9a and b), the corresponding pyrimidinediones (15a and b)(81–95%). The thiatriazepine (7a) reacts with sodium ethoxide to give a ring-opened product, believed to be 1-ethoxy-4-(2-thioxoimidazolin-1-yl)-1,4-diphenyl-2,3-diazabutadiene (18)(77%).