Department of Organic Chemistry, College of Chemistry, Beijing University of Chemical Technology, Beijing 100029, P. R. China
Abstract:
Semidines, including ortho-semidines and para-semidines, are generally byproducts in the benzidine rearrangements of N, N'-diarylhydrazines under acidic conditions. Under certain cases, for instance, N, N'-diarylhydrazines with substituted aryl substituents would give o- and p-semidines as major products. The π complex mechanism, and mechanisms involving cyclohexadiene cation intermediates and chloride-bridge-linked dication diradical pairs for the formation of semidines were proposed. However, by referring the data of kinetic isotope effect studies, theoretical and experimental investigations suggest that semidine rearrangements are sigmatropic shifts of pericyclic reactions with configuration-inverted N1, 3] sigmatropic shift as a key step. Mechanistic investigations and examples of semidine rearrangements are reviewed in this paper.
