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-fluoroethanone oximes 10 have been prepared by allowing the corresponding ketones to react with hydroxylamine hydroch loride in EtOH at room temperature, Stereochemical assignments for the oximes were made on the basis of H-1 NMR spectroscopic evidence and a n X-ray crystallographic analysis of 1-(3-chlorophenyl)-2,2-dichloroet hanone oxime 7f. The 1-aryl-2,2-dihalogenoethanone oximes react with t etrasulfur tetranitride in refluxing 1,4-dioxane to give 3-aryl-4-chlo ro-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 forma tion of the 1,2,5-thiadiazoles is proposed.