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

Abstract

AbstractSeveral 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.