1616514-75-0Relevant academic research and scientific papers
Regioselectivity of the ortho- and para-semidine, and diphenyline rearrangements
Yang, Zhanhui,Hou, Shili,He, Wei,Cheng, Baoxiang,Jiao, Peng,Xu, Jiaxi
, p. 2186 - 2195 (2016/04/09)
The regioselectivity of the o-semidine, p-semidine, and diphenyline rearrangements of unsymmetrical N,N′-diarylhydrazines was studied experimentally. The results indicate that their electron-rich nitrogen atom is first protonated and then the electron-poor non-protonated nitrogen atom undergoes an N[1,3]-sigmatropic shift to the ortho-position of the electron-rich aryl rings, generating key intermediates. The intermediates can undergo (1) a direct proton transfer to give o-semidines, (2) a second N[1,3]-shift of the electron-poor nitrogen atom and then proton transfer to furnish p-semidines, and (3) a [3,3]-sigmatropic shift and subsequent proton transfer to yield diphenylines. It is the first N[1,3]-sigmatropic shift step that plays an important role in controlling the regioselectivity in the three rearrangements, further determining the structures of o-semidines, p-semidines, and diphenylines. The current results provide new insights into the o/p-semidine and diphenyline rearrangements and useful information for controlling and predicting the structures of the rearrangement products.
N[1,3]-sigmatropic shift in the benzidine rearrangement: Experimental and theoretical investigation
Hou, Shili,Li, Xinyao,Xu, Jiaxi
, p. 4952 - 4963 (2014/07/07)
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. This journal is the Partner Organisations 2014.
