Examination of the Mechanism of Rh2(II)-Catalyzed Carbazole Formation Using Intramolecular Competition Experiments
摘要:
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 4 pi-electron-5-atom electrocyclization.
Rh2(II)-Catalyzed Synthesis of Carbazoles from Biaryl Azides
摘要:
An array of carbazoles (23 examples) can be synthesized from substituted biaryl azides at 60 degrees C using substoichiometric quantities of Rh-2(O2CC3F7)(4) or Rh-2(O2CC7H15)(4).