Stereoselectivity and Regioselectivity in Nucleophilic Ring Opening in Derivatives of 3-Phenylisoxazolo[2,3- a ]pyrimidine. Unpredicted Dimerization and Ring Transformation. Syntheses of Derivatives of Pyrimidinylmethylamine, Pyrimidinylmethylamino Acid Amides, and α-Amino-2-pyrimidinylacetamides 1