Tautomerism of azine derivatives. 5. Effect of the heteroatom on the keto-enol tautomerism of β-keto esters of the azine series

The effect of a nitrogen atom in various positions of the heteroaromatic ring on the ketol-enol equilibrium of 2-, 3-, and 4-pyridoyl-, 2- and 4-pyrimidoyl-, pyrazinoyl-, and 3- and 4-pyrazinoylacetic esters is examined. The anomalous effect of a nitrogen atom on the position relative to the tautomeric fragment is noted and is explained by interaction of the unshared pair of the nitrogen atom with the orbitals of the carbonyl group, which may lead to a decrease in the acceptor character of the azine substituent.See 1] for Communication 4. In Communication 4 Khim. Geterotsikl. Soedin., No. 6, p. 823 (1980)] there is a misprint in the scheme that illustrates the tautomeric equilibrium -keto esters with the participation of protonated forms. See 16] for the corrected scheme.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 530–535, April, 1981.