AMPLIFICATION OF DOUBLE STEREODIFFERENTIATION IN THE ASYMMETRIC HYDROGENATION BY A SOLVENT EFFECT

High diastereoselectivities of more than 96 % leading to (S)-amino acid menthyl esters were found in the hydrogenation of both the newly prepared enantiomers 3 and 4 of menthyl (Z)-2-N-benzoylamidocinnamate with the rhodium(I)-chelate of (Ph-beta-glup-OH) 1 as chiral catalyst in polar solvents, The analogous chelate of(Me-alpha-glup) 2 forms a mismached pair with the enantiomer 4 giving the (S)-product in a low diastereoselectivity which can be inversed in the apolar solvent benzene to 86 % of the (R)-diastereomer. Of particular note is the possibility of obtaining high yields either of(R)- or (S)-amino acids with the same catalyst with a single ligand derived from D-glucose.