The reaction of ortho-substituted aromatic azides with boron trichloride or trifluoride

Abstract

The reaction of boron trichloride or trifuoride with ortho-aryl, -diazoaryl, and -arylazoaryl phenyl azides in benzene at room temperature generally gives fused azoles in high yields. Treatment of 2-nitrophenyl azide with boron trichloride mainly affords chlorinated nitroanilines, whereas with boron trifluoride it gives N-o-nitrophenylaniline. In aromatic solvents at 60 °C in the presence of boron trifluoride–diethyl ether, 2-azidobiphenyl forms carbazole and 2-(arylamino)biphenyls, the formation of which depends greatly upon the nucleophilicity of the solvent used; however, its pseudo-first-order decomposition rate is slightly greater in benzene than in toluene or m-xylene. Under the same conditions, phenylazide forms diarylamines.

The results suggest that singlet nitrenium ions, arising from the corresponding azide–trihalogenoborane complexes by loss of molecular nitrogen, are generally the reactive intermediates.