Asymmetric Preparation of D-Phg-L-Pro Dipeptide-derived Chiral Ligands for Enantioselective Addition of Diethylzinc to Aldehydes

-Pro dipeptide analogues 2 and 3 as shown in Scheme1. The treatment of two diastereomeric mixture (1:1) of N-(α-bromo-α-phenylacetyl)-(L)-proline methyl ester 1 withan amine nucleophile (diphenylmethylamine or dibenzyl-amine) in the presence of tetrabutylammonium iodide (TBAI)and diisopropylethylamine (DIEA) in CH