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, eg, 2-amino-2H-isoxazolo [2, 3-~] pyrimidine system, was found to be unstable and to undergo rearrangement to 2-(cyanomethy1ene) pyrimidine 1-oxide derivatives. Kinetic study of this rearrangement at various pH values enabled the ...