?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; ZSUZSANA RIEDL ; GYÖRGY HAJÓS

Elsevier Science Ltd.

Año: 2005 vol. 61 p. 7489 - 7489

lash 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 8C. The only transformation observed up to 525 8C 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. q 2005 Elsevier Ltd. All rights reserved.