Novel Chiral Water Soluble Phosphines II. Application in Catalytic Asymmetric Hydrogenation

Article abstract of DOI:10.1016/S0957-4166(00)82282-X

The results of the homogeneous asymmetric hydrogenation of several dehydroamino acids by rhodium-diene complexes of the chiral ligands; 2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(bis(p-N,N-dimethylaminophenyl)phosphino)butane, 2a; 2,4-bis(bis(p-N,N-dimethylaminophenyl)phosphino)pentane, 3a; 2,3-bis(bis(p-N,N-dimethylaminophenyl)phosphino)butane, 4a; and their N-protonated and N-Me quaternized analogues are reported.The ligands comprise a versatile set which can be used both in organic and aqueous solvents.A detailed investigation of solvent and substituent effects isprovided.The presence of p-NMe2 groups enhances the rate of reaction in all cases.For the DIOP derivative, 2a, the presence of the dimethylamino group causes a reversal in the observed dominant product antipode.This is attributed predominantly to a change in preferred ligand conformation rather than to a kinetic difference between the two diastereomers of a single ligand conformation.