Flash vacuum pyrolysis reactions of [1,2,4]triazolo[3,4-c][1,2,4]benzotriazines 1 a-d were carried out as part of our studies on thermal reactivity of [1,2,4]benzotriazines [1]. When these compounds were subjected to f.v.p. in a conventional flow system (500 ºC, contact times of ~10-2s) isomerization to [1,2,4]triazolo[4,3-b][1,2,4]benzotriazines 3 a-d was observed. At higher temperatures, fragmentation to the corresponding benzonitriles 4 a,b,d was found as a consecutive reaction. According to experimental kinetic parameters depicted in Table 1, the most probable mechanism is a concerted [1,3] sigmatropic shift to the 1H-diazirene 2 a-d. The Arrhenius values agree with previously reported ones for f.v.p. isomerization of isoxazoles to 1-azirines [2, 3].
1.Riedl, Z., Hajós, Gy., Peláez, W., Gafarova, I., Moyano, E., Yranzo, G.; Tetrahedron, 2003, 59, 851.
2.Pérez, J. D., de Díaz, R. Yranzo, G. I. ; J. Org. Chem., 1981, 46, 3502-3508.
3.Pérez, J. D., Yranzo, G. I. Wunderlin, D. A.; J. Org. Chem., 1982, 47, 982-984.
