d-Phg-l-Pro Dipeptide-derived prolinol ligands for highly enantioselective Reformatsky reactions

Optically pure N-aminoethyl prolinol derivatives 3a–c have been prepared from the dynamic kinetic resolution of N-(α-bromo-α-phenylacetyl) proline ester 1 in asymmetric nucleophilic substitution and subsequent reduction. The peptide-derived prolinols are tested as chiral ligands in the asymmetric addition of Reformatsky reagent to aromatic aldehydes. Chiral ligand 3c has been shown to be effective to produce enantioenriched β-hydroxy esters 5a–j with up to 98% ee.