Stokes Benjamin J, Richert Kathleen J, Driver Tom G
Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607-7061, USA.
J Org Chem. 2009 Sep 4;74(17):6442-51. doi: 10.1021/jo901224k.
The use of a rhodium(II) carboxylate catalyst enables the mild and stereoselective formation of carbazoles from biaryl azides. Intramolecular competition experiments of triaryl azides suggested the source of the selectivity. A primary intramolecular kinetic isotope effect was not observed, and correlation of the product ratios with Hammett sigma(+) values produced a plot with two intersecting lines with opposite rho values. These data suggest that electronic donation by the biaryl pi-system accelerates the formation of rhodium nitrenoid and that C-N bond formation occurs through a 4pi-electron-5-atom electrocyclization.
使用羧酸铑（II）催化剂能够温和且立体选择性地从联芳基叠氮化物形成咔唑。三芳基叠氮化物的分子内竞争实验表明了选择性的来源。未观察到一级分子内动力学同位素效应，并且产物比例与哈米特σ(+)值的相关性产生了一个具有两条相交线且ρ值相反的图。这些数据表明联芳基π体系的电子给予加速了铑氮宾的形成，并且C-N键的形成是通过4π电子-5原子电环化反应进行的。
