Thermal Ring-Opening of Pyrazolo[3,4- d ][1,2,3]triazin-4-ones: An Experimental and Theoretical Study

COLOMER, JUAN P.; SCIÚ, MARÍA L.; RAMIREZ, CRISTINA L.; SORIA-CASTRO, SILVIA M.; VERA, D. MARIANO A.; MOYANO, ELIZABETH L.

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY

WILEY-V C H VERLAG GMBH

Año: 2018

1434-193X

Abstract:Several 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 anitrogen 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 ofpyrazolotriazinone. The complete and detailed mechanism of product formation involving the iminoketene intermediate and all other reasonable pathways as well, were explored withDFT calculations. Furthermore, additional experimental studies to corroboratethe presence of iminoketene intermediate were carried out.