EPR and pulsed ENDOR study of intermediates from reactions of aromatic azides with group 13 metal trichlorides

• Giorgio Bencivenni,
• Riccardo Cesari,
• Daniele Nanni,
• Hassane El Mkami and
• John C. Walton

Beilstein J. Org. Chem. 2010, 6, 713–725, doi:10.3762/bjoc.6.84

• ], and δ-azidoesters and chlorides into allylated nitrogen heterocycles [30]. To help in elucidating the mechanisms of these reductions, we used CW EPR spectroscopy and attempted to characterise the reactive intermediates in selected reactions involving gallium trichloride. Surprisingly, we found that

• treatment of phenyl azide and 4-methoxyphenyl azide with gallium trichloride resulted in strong EPR spectra of long-lived paramagnetic species. By combining the results of product analyses with the results of EPR spectroscopy, we were able to show that persistent radical cations of ‘dimers’ (4

• the broad component. No reaction of 4-azidobenzonitrile 7 with InCl3, GaCl3 or AlCl3 was observed and no paramagnetic species were detected by EPR spectroscopy. It appears the electron-accepting property of the CN group inhibited the coupling process at some stage. It is also worth mentioning that, as