Dynamic Resolution of α-Bromo-α-Alkyl Esters Using N-Methyl Pseudo-ephedrine as a Chiral Auxiliary: Asymmetric Syntheses of α-Amino Acid Derivatives

N-Methyl pseudoephedrine mediated dynamic resolution of α-bromo-α-alkyl esters in nucleophilic substitution reaction has been investigated. Best results are obtained when α-bromo-α-alkyl esters 1, 4 and 5 are allowed to equilibrate before the addition of nucleophile. This simple epimerization-substitution sequence provides a practical protocol for asymmetric syntheses of α-amino acid derivatives 2, 7 and 8 up to 98:2 enantiomeric ratio.