Absence of triazirine intermediates in the photolytic formation of azides from mesoionic 3-substituted 1,2,3,4-oxatriazolylio-5-oxides : Isotope labelling experiments

Irradiation of 3-phenyl-1,2,3,4-oxatriazolylio-5-oxide (1) leads to formation of CO₂, N₂O, phenyl azide and phenyl isocyanate. The two latter compounds are observed only in low yields because of secondary photolytic reactions. Photolysis in CCl₄ or Cl₂CCCl₂ of 2-¹⁵N labelled (1) leads almost exclusively to the formation of 3-¹⁵H labelled phenyl azide identified by IR spectroscopy on comparison with authentic 1-¹⁵N, 2-¹⁵N and 3-¹⁵N labelled phenyl azides, respectively. These results show that phenyl azide is formed photolytically from (1) via phenyl migration and not via “antiaromatic”, phenyl triazirine (2).