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

Abstract

Trithiazyl trichloride 1 converts primary and secondary enamines, enamides and 1,2,3-triazoles into 1,2,5-thiadiazoles. These mild reactions provide one-pot routes to various alkyl, aryl, functional and quaternary 1,2,5-thiadiazoles, in moderate to good yields. The trimer 1 reacts as a 1,2-bis-electrophile adding an N–S unit across CC–N. For primary enamines ¹⁵N-labelling reveals an additional, minor pathway in which N–S–N is added across CC, with elimination of the enamine nitrogen. With N-alkylated enamines the alkyl group is retained in a quaternised thiadiazole, but this can be dealkylated insitu. 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.