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 vol. 2018 p. 1514 - 1524

1434-193X

Several 3-pyrazolylcarbonyl-pyrazolo[3,4-d][1,2,3]triazin-4-ones have been prepared from 5-amino-1H-pyrazole-4-carbonitriles through a simple sequence. In the first step,diazotization of the corresponding aminopyrazoles affordedpyrazolo[3,4-d][1,2,3]triazin-4-ones. Next, thermal rearrangementof these compounds through nitrogen elimination gavethe final products. The proposed mechanism for the ring-openingof the pyrazolotriazinones to give the pyrazolylcarbonylpyrazolotriazinones involves the generation of an iminoketeneintermediate, which reacts with a second molecule of pyrazolotriazinone.The complete mechanism of product formation involvingthe iminoketene intermediate, and all other reasonablepathways, have been explored in detail through DFT calculations.Furthermore, additional experiments to corroborate thepresence of the iminoketene intermediate were carried out.