Reaction of tetracyanoethylene with SCl1

Abstract

The chloride ion catalysed addition of SCl2 to TCNE gives the 4-dicyanomethylene-l,2,6-thiadiazine 2 (60%) with two minor products (5%) of extensive molecular rearrangement, the pyrimidine 4 and the pyrroloimidazothiadiazine 5. Mechanisms proposed for the formation of all three products involve the interaction of SCl2 with one cyano group and neighbouring group participation by geminal and vicinal cyano groups. The dicyanomethylene thiadiazine 2 reacts further with SCl2 to give the pyrrolo-l,2,6-thiadiazine 19. The two chlorine atoms of the pyrroloimidazothiadiazine 5 are successively replaced by pyrrolidine to give the substitution products 20 and 21 in high yield. 1H and 13C NMR spectra show that rotation of the pyrrolidine ring on the thiadiazine is considerably slower than for that on the pyrrole ring, and there is electron delocalisation across the new 147t tricyclic heteroaromatic system. © The Royal Society of Chemistry 2000.