New Approach to the Coupling of γ-Amino β-Hydroxy Acids and β,γ-Dihydroxy Acids with α-Amino Acid Esters

α,α-Dichloro β-lactones, readily obtained by a highly diastereoselective cycloaddition of dichloroketene to N -Boc-α-amino aldehydes and α-(silyloxy) aldehydes, coupled efficiently with α-amino acid esters leading, after dehalogenation with H 2 over 10% Pd on charcoal, to peptide mimics under mild reaction conditions.