Unexpected valence bond isomerization of [1,2,4]triazolo[3,4-c][1,2,4] benzotriazines under flash vacuum pyrolytic (fvp) conditions

Walter J. Peláez, Gloria I. Yranzo, Csilla Gróf, Zsuzsanna Riedl, György Hajós

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Flash vacuum pyrolysis (fvp) of some substituted [1,2,4]triazolo[3,4-c][1, 2,4]benzotriazine derivatives (1a-d) has been studied between 450 and 600°C. The only transformation observed up to 525°C was the unexpected valence bond isomerization of the angularly fused starting compounds to the isomeric linearly fused [1,2,4]triazolo[4,3-b][1,2,4]benzotriazine derivatives (9a-d), whereas at higher temperatures fragmentation products such as aromatic nitriles were also formed. Kinetic measurements revealed negative entropies of activation in the isomerization process, which suggest a concerted ring closure reaction to an intermediate antiaromatic diazirine. Reversibiblity of the title isomerization reaction was also proved by FVP experiments.

Original languageEnglish
Pages (from-to)7489-7498
Number of pages10
Issue number31
Publication statusPublished - Aug 1 2005



  • Azirine intermediate
  • Enthropy of activation
  • Flash vacuum pyrolysis
  • Sigmatropic rearrangement
  • Valence bond isomerisation

ASJC Scopus subject areas

  • Biochemistry
  • Drug Discovery
  • Organic Chemistry

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