title: N[1,3]-Sigmatropic shift in the benzidine rearrangement: experimental and theoretical investigation.
abstract: The N[1,3]-sigmatropic shift in the benzidine rearrangement has been studied in depth experimentally with the aid of density functional theory (DFT) calculations. The designed substituted N,N'-diaryl hydrazines rearrange exclusively to the expected o/p-semidines and diphenylines. Intercrossing experiments support the intramolecular rearrangement process. Radical trapping experiments exclude the intermediacy of biradicals in the rearrangements. Computational results demonstrate that the o-semidine rearrangement involves a novel N[1,3]-sigmatropic shift and the p-semidine rearrangement proceeds via tandem N[1,3]/N[1,3]-sigmatropic shifts, while the diphenyline rearrangement occurs through cascade N[1,3]/[3,3]-sigmatropic shifts. The proposed mechanism involving the key N[1,3]-sigmatropic shift as the rate-limiting step is in good agreement with reported kinetic isotope measurements. The combined methods provide new insight into the formation mechanism of o/p-semidines and diphenylines in the benzidine rearrangement and support the unprecedented suprafacial symmetry allowed N[1,3]-sigmatropic shift with an inversion of the configuration in the migrating nitrogen atom.
authors.affiliation: State Key Laboratory of Chemical Resource Engineering, Department of Organic Chemistry, Faculty of Science, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China. jxxu@mail.buct.edu.cn.
authors.forename: Shili
authors.initials: S
authors.lastname: Hou
authors.forename: Xinyao
authors.initials: X
authors.lastname: Li
authors.forename: Jiaxi
authors.initials: J
authors.lastname: Xu
mesh_terms: D001560:Benzidines / Q000737:chemistry*; D002384:Catalysis; D006834:Hydrazines / Q000737:chemistry*; D010655:Phenylenediamines / Q000737:chemistry*
chemical_list: D001560:Benzidines; D006834:Hydrazines; D010655:Phenylenediamines; C031506:4-aminodiphenylamine; C029876:benzidine