Study of the diazoimine/triazole equilibria for substituted thiazoles and thiadiazoles

Several diazomethyl and diazoester substituted thiazoles and thiadiazoles were prepared and their ring/chain equilibria studied by nmr spectroscopy. The diazomethyl derivatives 17a,b,d and 19a exist predominantly or exclusively in the triazole form. Ring-opening is promoted by introducing an ester group at the diazo function (17c,e, 19b, 21) or by changing thiazoles for thiadiazoles in the following order: thiazole < 1,3,4-thiadiazole < 1,2,4-thiadiazole. The diazoimine/triazole equilibria are also shifted towards the diazo form by raising the temperature and by using less polar solvents in the order: dimethyl sulfoxide < acetonitrile < chloroform < benzene. The ir spectra (potassium bromide discs) of the compounds indicate that they all, except 21 , exist in the crystalline state in the triazole form.