Reactions of monohalomethyl aryl ketoximes with tetrasulfur tetranitride: much improved synthesis of 3-aryl-1,2,5-thiadiazoles

Reactions of chloromethyl aryl ketoximes (1, X = Cl) with tetrasulfur tetranitride in p-dioxane at reflux for 4 h afforded 3-aryl-1,2,5-thia- diazoles (2) in 37-92% yields, whereas those of bromo analogs under the same conditions gave 2 and 3-aryl-4-bromo-1,2,5-thiadiazoles (3) in 48- 81% and 17-31% yields, respectively. However, the compounds (3) were not formed in the presence of pyridine. α-Nitrosostyrene and its ring- substituted derivatives (4) are proposed as intermediates for the forma- tions of 2