BASE-CATALYZED TRANSFORMATIONS OF IMINIUM PHENYLHYDRAZONES. A NEW CONVENIENT SYNTHESIS OF IMIDAZOAZACYCLOALKANES

Article abstract of DOI:10.1016/S0040-4020(01)98869-6

β-Enamine esters react with phenyldiazonium fluoroborate to give iminium phenylhydrazone salts which, without isolation, can be converted by a base-catalysed reaction to imidazole derivatives.The latter reaction is critically dependent upon the nature of the base-component of the enamine ester.The mechanism of imidazole formation involves the following sequence of steps: (a) deprotonation of the iminium salt, (b) a symmetry-allowed 1,5-dipolar cyclization of the betaine intermediate and (c) subsequent elimination of aniline, whith concomitant aromatization.The scope of the reaction as a facile approach to the synthesis of imidazole derivatives is discussed.