Diastereoselective Synthesis of α-Methyl and α-Hydroxy-β-Amino Acids via 4-Substituted-1,3-Oxazinan-6-ones

1,3-oxazinan-6-ones have been utilized in a series of enolate reactions to produce 5-hydroxy and 5-alkyl-4-substituted-1,3-oxazinan-6-ones with excellent trans diastereoselectivity. Highlighting the versatility of the oxazinanone, a number of transformations were performed to produce a variety of protected N-H and N-methyl alpha-hydroxy- and alpha-methyl-beta-amino acids.