An unambiguous synthesis of pyrazoles by sulphur extrusion from 1,2,6-thiadiazines

Abstract

Di-imines (1) react with thionyl chloride and sulphur monochloride and dichloride giving different 1,2,6-thiadiazine S-oxides (3) and 1,2,6-thiadiazines (4), respectively. These last two compounds lead, by heating, to pyrazoles (6)via thermal extrusion of sulphur oxide or sulphur. On the other hand, 1,2,6-thiadiazine S-dioxides (5), which can be obtained by oxidation of (3) or (4), do not undergo the extrusion of sulphur dioxide.