Azoles and azines. 62. Structure of 2-aryl-1,3-oxazine-4,6-diones

Abstract

1H,13C NMR, IR, and UV spectra have been studied for solutions of a number of potentially tautomeric 2-aryl-1,3-oxazine-4,6-diones and their 5-methyl substituted analogs with variation of substituent at the para position of the benzene ring, as well as compounds with a fixed structure that simulates possible tautomeric forms. The data have been compared with the results of quantum chemical calculations carried out in SSO MO LCAO approximation by the CNO, CNDO/2, and MPNDO/3 methods. In DMSO and THF solution the test compounds exist predominantly as 2-aryl-4-hydroxy-6H-1,3-oxazin-6-ones. The para substituent in the benzene ring does not affect the composition of the tautomer mixture significantly.