Intermolecular alkyl/aryl exchange of 2-iminothiazoles with isothiocyanates and isocyanates: scopes and limitations

2-Iminothiazole, an isoform of 2-aminothiazole, is a scaffold of synthetic and medicinal significance. We have reported an efficient method by which alkyl group of 2-alkyliminothiazoles is changed into other alkyl groups by isothiocyanates. In this article, a detailed mechanistic aspect, and the scopes and limitations were disclosed. All the reactions were carried out in toluene at 105 °C without any additive. The reaction is a reversible process and the equilibrium is determined by the reactivity of both reactants, in which the more electron-withdrawing alkyl or aryl groups at the 2-imino group or isothiocyanate showed higher reactivities. With this simple method, we effectively altered the alkyl group attached on the imine nitrogen. A synthetic problem in 2-iminothiazole chemistry, synthesis of amino acid-derived 2-iminothiazole was solved in a very simple manner. Using suitably designed 2-iminothiazole substrate, the electrophilic reactivity of various isothiocyanates could be empirically compared by this exchange reaction. Moreover, successful exchange reaction using isocyanates instead of isothiocyanates broadened the utility of this reaction.