Investigation of azoles and azines. 75. Structure of 2-aryl-1,3-oxazine-4,6-diones in the gas phase

The mass-spectrometric fragmentation of a number of potentially tautomeric 2-aryl-1,3-oxazine-4,6-diones and model substances that fix the possible tautomeric forms was studied. The characteristic fragmentation pathways that are peculiar to one or another tautomer and the characteristic ions that make it possible to identify them in tautomeric mixtures were ascertained. It is shown that in the gas phase 2-aryl-1,3-oxazine-4,6-diones exist in mixtures of 4-hydroxy, 6-oxo, dipolar-ionic, and dicarbonyl forms; the amounts of the latter two forms increase with intensification of the electron-acceptor properties of the substituent in the para position of the benzene ring.See [1] for Communication 74.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 552–556, April, 1990.