Reactive intermediates. Part XXV. Investigation of the pyrolysis of 1,4- and 1,5-diphenyl-1,2,3-triazoles by use of 13C-labelled compounds
Abstract
1,4-Diphenyl-[4-13C]1,2,3-triazole (1) and 1,5-diphenyl-[5-13C]1,2,3-triazole (2) have been prepared by the addition of azidobenzene to phenyl[1-13C]acetylene. Pyrolysis of the triazoles in the vapour phase gave the same four compounds in each case: 1-, 2-, and 3-phenylindole, and N-(phenylvinylidene)aniline, which was isolated as its hydrolysis product, phenylacetanilide. It has also been established that 1-, 2-, and 3-phenylindoles can be interconverted by vapour phase pyrolysis. 13C N.m.r. spectra of these indoles, and of phenylacetanilide, are reported. An analysis by fast Fourier transform 13C n.m.r. of the positions of 13C enrichment in the products derived from the triazoles has shown a substantial degree of scrambling of the 13C label in the products derived from 1,5-diphenyl-[5-13C]1,2,3-triazole, which provides strong evidence for the intermediacy of a 1H-azirine in the reactions. The products derived from 1,4-diphenyl-[4-13C]1,2,3-triazole show little or no scrambling of the label.