Identification of a triple-stereodifferentiation effect using ( R )/( S )-propylene glycol 22 as the asymmetric linker in a diastereoconvergent reaction of racemic phenylalanine N -carboxyanhydride 23 using (DHQD) 2 AQN as catalyst. DMAP, 4-(dimethylamino)pyridine; Et 2 O, diethyl ether. a e.e. values were determined from the corresponding methyl esters, after hydrolysis and methylation using KHCO 3 and CH 3 I; for full details, see section 5 of the Supplementary Information.
