The thermolysis of polyazapentadienes. Part 5. Degenerate rearrangement of aryliminoiminyl radicals: a 15N-labelling study

Abstract

The ¹⁵N n.m.r. spectra of 5- and 6-methylquinoxaline are unambiguously interpreted by the synthesis and spectra of specifically ¹⁵N-labelled quinoxalines. The results are compared with the ¹³C n.m.r. spectra of analogous naphthalenes. Pyrolysis of [2-¹⁵N]- or [5-¹⁵N]-1-phenyl-5-p-tplyl-1,2,5-triazapentadiene gives an unequal mixture of [1-¹⁵N]- and [4-¹⁵N]-6-methylquinoxaline owing to equilibration of the intermediate aryliminoiminyl radical via a spirodienyl radical to the extent of ca. 88%. 5- and 6-Methyl-quinoxaline obtained from the [2-¹⁵N]-5-m-tolyl analogue show evidence of rearrangement to the extent of 72 and 80% respectively while the distribution of label in 5-methylquinoxaline obtained from the corresponding [2-¹⁵N]-5-(2,6-dimethylphenyl) compound suggests almost complete involvement of the spirodienyl in this case.