Molecular Rearrangements. Synthesis, Stability, and Rearrangements of 2-Imino-2H-isoxazolo[2,3-a]pyrimidines and 2-Aminoisoxazolo[2,3-a]pyrimidinium Salts

2-Amino derivatives of isoxazolo[2,3-a]pyrimidinium salts were prepared by the condensation of 3,5-diaminoisoxazole with acetylacetone and benzoylacetone, respectively. The free base, e.g., 2-amino-2/f-isox-azolo[2,3-o]pyrimidine system, was found to be unstable and to undergo rearrangement to 2-(cyanomethylene)pyrimidine 1-oxide derivatives. Kinetic study of this rearrangement at various pH values enabled the determination of the mechanism of the reactions and the dissociation constants of these compounds. An acetyl group on the amino group inhibited the reaction. The system having a phenyl group at position 3 also proved to be resistant to this kind of decomposition. 2-Immo-3-phenyl-5,7-dimethyl-2H-isoxazolo[2,3-a]pyrimidine underwent different kinds of rearrangements upon heating with HC1, acetic anhydride, or ethanol, respectively. 3,5-Diamino-4-phenylisoxazole was prepared by two steps from 2-phenylmalononitrile.