Criteria for the cation radical vs. electrophilic mechanistic distinction: the aminium salt-catalysed Diels–Alder reaction

Abstract

The tris(4-bromophenyl)aminium salt-catalysed Diels–Alder additions of stilbenes to 2, 3-dimethylbuta-1,3diene are shown to proceed via ionization of the stilbenes to the corresponding cation radicals by demonstrating that the reactions involve the generation of a unit positive charge in an essentially symmetrical distribution on the stilbene substrates; a hypothetical electrophilic mechanism is unequivocally ruled out by the present results.