Cycloaddition reactions of diiminosuccinonitrile (DISN) with nucleophilic olefins yield a variety of products including [4+ 21 cycloadducts and aziridines. All of the products derived from l, &dienes, styrene, para-substituted styrenes, cycloheptatriene, norbornene, and norbornadiene can be accounted for by rearrangements of a common intermediate, zwitterionic aziridinium ion. We introduce the concept of reverse polarization and propose ...