Synthesis of Some 1H-1,2,4-Triazole, 4H-1,2,4-Triazole, Thiazolo[2,3-c]-1,2,4-triazole and 5H-1,2,4-Triazolo-[3,4-b][1,3]thiazine Derivatives by Metal Compound-Mediated Oxidative Cyclization of Derivatives of 2-(Phenylmethylidene)hydrazinecarboximidothioic Acid

Abstract

Reaction of the methyl 2-(phenylmethylidene)hydrazinecarboximidothioate derivatives (3a–d) and (6a,b) with iron(III) chloride afforded the 5-methylsulfanyl-3-phenyl-4H-1,2,4-triazole derivatives (4a–d) and the 5-methylsulfanyl-3-phenyl-1H-1,2,4-triazole derivatives (7a,b). This reaction was extended to the synthesis of the 3-phenyl-5,6-dihydrothiazolo[2,3-c]-1,2,4-triazole derivatives (10a,b) and the 3-phenyl-6,7-dihydro-5H-1,2,4-triazolo[3,4-b][1,3]thiazine derivatives (10c,d). Reaction of 5-(3-chlorophenyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione (12a) with 1,2-dibromoethane gave (10a) together with the isomeric 2-(3-chlorophenyl)-5,6-dihydrothiazolo[3,2-b][1,2,4]triazole (13a); similarly, reaction of (12a) with 1,3-dibromopropane afforded (10c) along with 2-(3-chlorophenyl)-6,7-dihydro-5H-[1,2,4]triazolo[5,1-b][1,3]thiazine (13b). The use of nickel peroxide and lead tetraacetate in place of iron(III) chloride was investigated for some of these oxidative cyclization reactions.