Synthesis and Rearrangement of 2-Oxo-3-phenylisoxazolo[2,3-α]pyrimidines

2-Oxo-3-phenylisoxazolo[2,3-α]pyrimidine derivatives were synthesized by the reaction of 3-amino-4-phenyl-5-isoxazolone with malonaldehyde tetraacetal, 3-oxobutyraldehyde diacetal, 2,4-pentanedione, and 1-phenyl-1,3-butanedione. The regioselectivity of this reaction was determined by X-ray single crystal structural analysis. Upon heating either in water or in ethanol this bicyclic system underwent a ring opening, followed by decarboxylation to yield phenylpyrimidylmethanol and phenylpyrimidyl methyl ethers. The structures of these 2-oxoisoxazolo[2,3-α]pyrimidines and the mechanism of their rearrangement is discussed.