Reactions of 1-aryl-2,2-dihalogenoethanone oximes with tetrasulfur tetranitride (S4N4): a general method for the synthesis of 3-aryl-4-halogeno-1,2,5-thiadiazoles

1-Aryl-2,2-dichloro-7, 1-aryl-2,2-dibromo-8, 1-aryl-2-bromo-2-fluoro-9 and 1-aryl-2-chloro-2-fluoro-ethanone oximes 10 have been prepared by allowing the corresponding ketones to react with hydroxylamine hydrochloride in EtOH at room temperature. Stereochemical assignments for the oximes were made on the basis of 1H NMR spectroscopic evidence and an X-ray crystallographic analysis of 1-(3-chlorophenyl)-2,2-dichloroethanone oxime 7f. The 1-aryl-2,2-dihalogenoethanone oximes react with tetrasulfur tetranitride in refluxing 1,4-dioxane to give 3-aryl-4-chloro-1, 3-aryl-4-bromo-2, and 3-aryl-4-fluoro-1,2,5-thiadiazoles 3 in 69–98, 49–99, and 32–65% yields, respectively. A mechanism for the formation of the 1,2,5-thiadiazoles is proposed.