Examination of the mechanism of Rh(2)(II)-catalyzed carbazole formation using intramolecular competition experiments.
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.
Stokes
Benjamin J
BJ
Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607-7061, USA.
Richert
Kathleen J
KJ
Driver
Tom G
TG
D001386:Azides / Q000737:chemistry; D001667:Binding, Competitive; D002227:Carbazoles / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry; D002384:Catalysis; D002625:Chemistry, Organic / Q000379:methods*; D004583:Electrons; D007554:Isotopes; D007700:Kinetics; D008956:Models, Chemical; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry; D012238:Rhodium / Q000737:chemistry*
D001386:Azides; D002227:Carbazoles; D007554:Isotopes; D002244:Carbon; D012238:Rhodium; D009584:Nitrogen