Conversion of enamines, enamides and triazoles by trithiazyl trichloride into 1,2,5-thiadiazoles

Trithiazyl trichloride 1 converts primary and secondary enamines, enamides and 1,2,3-triazoles into 1,2,5-thiadiazoles. These mild reactions provide o ne-pot routes to various alkyl, aryl, functional and quaternary 1,2,5-thiad iazoles, in moderate to good yields. The trimer 1 reacts as a 1,2-bis-elect rophile adding an N-S unit across C=C-N. For primary enamines N-15-labellin g reveals an additional, minor pathway in which N-S-N is added across C=C, with elimination of the enamine nitrogen. With N-alkylated enamines the alk yl group is retained in a quaternised thiadiazole, but this can be dealkyla ted in situ. Enamides react similarly but with spontaneous N-deacylation. 1 ,2,3-Triazoles with electron withdrawing groups to stabilise their acyclic diazoimine tautomers also give 1,2,5-thiadiazoles, with loss of dinitrogen. Mechanisms are proposed for these new reactions.