Thermal ring opening of pyrazolo[3,4-d][1,2,3]triazin-4-ones: an experimental and theoretical study

J. P. COLOMER; M. L. SCIU; C. L. RAMIREZ; S. M. SORIA CASTRO; D. M. A. VERA*; E. L. MOYANO

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY

WILEY-V C H VERLAG GMBH

Lugar: Weinheim; Año: 2018 vol. 2018 p. 1514 - 1524

1434-193X

Several 3-pyrazolecarbonyl-pyrazolo[3,4-d][1,2,3]triazin-4-ones were prepared from 5-amino-1H-pyrazole-4-carbonitrilesthrough a simple sequence. In a first step, diazotization ofaminopyrazole afforded pyrazolo[3,4-d][1,2,3]triazin-4-ones. Next, athermal rearrangement of these compounds through a nitrogenelimination gave the final products. The proposed mechanism for thering opening of pyrazolotriazinones to give the pyrazolecarbonyl-pyrazolotriazinones includes the generation of an iminoketeneintermediate, which reacts with a second molecule ofpyrazolotriazinone. The complete and detailed mechanism of productformation involving the iminoketene intermediate and all otherreasonable pathways as well, were explored with DFT calculations.Furthermore, additional experimental studies to corroborate thepresence of iminoketene intermediate were carried out.