Hydrazinolysis of 3-R-[1,2,4]triazino[2,3-c]quinazolin-2-ones. Synthetic and theoretical aspects.

It has been shown that heating of 3-R-[1,2,4]triazino[2,3-c]quinazolin-2-ones with 5-fold excess of hydrazine hydrate in propanol-2 gave the corresponding 3-(2-aminophenyl)-6-R-1,2,4-triazin-5-ones with high yields. The mechanism of the reaction has been proposed based on the results of theoretical investigation at B3LYP and MP2 levels of theory. According to calculations, an attack of the hydrazine molecule on the C6═N7 double bond leads to ring-opening with N5-C6 bond cleavage. The process continues by addition of the second nucleophile molecule and elimination of the formazan fragment through a series of transformations that yield the target product.