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

COLOMER, JUAN PABLO; SCIÚ, MARÍA LOURDES; RAMIREZ, CRISTINA; SORIA CASTRO, SILVIA; VERA, DOMINGO MARIANO; MOYANO, ELIZABETH LAURA

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY

WILEY-V C H VERLAG GMBH

Año: 2018 vol. 2018 p. 1514 - 1514

1434-193X

everal 3-pyrazolecarbonyl-pyrazolo[3,4-d][1,2,3]triazin-4-ones were prepared from 5-amino-1H-pyrazole-4-carbonitriles through a simple sequence. In a first step, diazotization of aminopyrazole afforded pyrazolo[3,4-d][1,2,3]triazin-4-ones. Next, a thermal rearrangement of these compounds through a nitrogen elimination gave the final products. The proposed mechanism for the ring opening of pyrazolotriazinones to give the pyrazolecarbonyl-pyrazolotriazinones includes the generation of an iminoketene intermediate, which reacts with a second molecule of pyrazolotriazinone. The complete and detailed mechanism of product formation involving the iminoketene intermediate and all other reasonable pathways as well, were explored with DFT calculations. Furthermore, additional experimental studies to corroborate the presence of iminoketene intermediate were carried out.