Pyrazole from thiadiazine 1-oxides

The extrusion of SO from some 1,2,6-thiadiazine 1-oxides, such as 198, to give the corresponding pyrazole can be achieved by heating in toluene [79CC891 81JCS(P1)1891 83JCS(P 1)2273]. The reaction of bromine/ dichloromethane with 3-oxo l,2,5-thiadiazine212(R = Me, R2 = Me) in... 

Diimines 1 react with sulfur dichloride or disulfur dichloride to give the 1,2,6-thiadiazines 2aj.23 When compounds 1 are treated with thionyl chloride, the 1,2,6-thiadiazine S-oxides 3a-l are formed.23,24 On heating in toluene to 90°C, compounds 2a-j are converted into the pyrazoles 4 by extrusion of sulfur. The pyrazoles 4 can also be obtained by heating the diimines 1 in pyridine for 8 hours with sulfur dichloride, disulfur dichloride, or thionyl chloride. In contrast, the tetrahydro-l,2,6-thiadiazines23 obtained from 1,3-diamines and sulfur dichloride cannot be converted to pyrazolidine derivatives by extrusion of sulfur. When compounds 2 a j or 3a-l are heated at 60 °C in tetrahydrofuran containing 6M potassium hydroxide, the starting materials 1 are recovered. 

---