Thermal rearrangement of 4-iminomethyl-1,2,3-thiadiazoles

Abstract

Imines derived from 1,2,3-thiadiazole-4-carbaldehyde 4 rearrange thermally into 1,2,3-triazole-4-thiocarbaldehydes 6 which were trapped with anthracene or 2.3-dimethylbutadiene. In two cases, 1,2,3-thiadiazole-4-thiocarbaldehyde 9 was intercepted as the Diels–Alder adduct 11. 5-Phenyl-1,2,3-thiadiazole-4-carbaldehyde 14 reacts with amines to give 4-benzoyl-1,2,3-triazoles 17via the intermediate 4-thiobenzoyltriazoles 16, whose existence has been demonstrated by NMR. The reactions of 5-tert-butylthio-1,2,3-thiadiazole-4-carbaldehyde 18 with amines yield either 1,2,3-triazole-4-dithio esters 20 or 1,2,3-triazole-4-thioamides 21. In solution, the dithioesters 20 equilibrate with the imines 19 when the R-substituent is aryl. From the reaction conditions we conclude that the facility of rearrangement of the title compounds depends on the nucleophilicity of the imine nitrogen and on the 5-substituent in the order Bu^tS > Ph > H.