Studies on Pyrimidine Derivatives. XIV. On the Structural Determination of Pyrimidine N-Oxides

N-Oxidation of pyrimidines having unsymmetrically substituted 4-and 6-positions with hydrogen peroxide in acetic acid gave mixture of their 1-oxides and 3-oxides. Ring transformation of these 1-oxides and 3-oxides into isoxazoles occurred on treatment with mineral acid, and provided information on the position of the N-oxide group in the pyrimidine N-oxides. Nuclear magnetic resonance spectroscopy with a lanthanide shift reagent was also found to be useful in identifying the pyrimidine 1-and 3-oxides.