One-step syntheses of pyrrolo- and indolo-1,2,5-thiadiazoles and pyrrolobis[1,2,5]thiadiazoles

Abstract

Treatment of the 2,3-unsubstituted pyrrole 2 and indoles 7 with trithiazyl trichloride 1 in hot tetrachloromethane gives the 2,3-fused 1,2,5-thiadiazolo derivatives 3 and 8. 2,3,4,5-Unsubstituted pyrroles 4 are similarly converted directly into the pyrrolobis(thiadiazoles) 6, without detection of the presumed, highly reactive, bicyclic intermediate 5. This ring fusion process is not prevented by the presence of bromine, chlorine, a carboxylic acid or carboxylic ester group at the α- or β-positions; indeed prior substitution by bromine or chlorine results in faster and cleaner reactions with trithiazyl trichloride to give the fused systems 3, 6 and 8 in high yield. Possible mechanisms are proposed to explain these results.