R. Selke, H. Pracejus
Oct 1, 1986
Citations
0
Influential Citations
85
Citations
Quality indicators
Journal
Journal of Molecular Catalysis
Abstract
Abstract Phenyl 4,6-O-(R)-benzylidene-2,3-O-bis(diphenylphosphino)-β-D-glucopyranoside (Ph-β-glup) 4a, a new air-stable chiral bidentate ligand, is easily prepared from glucose. Its cationic rhodium(I) chelate 5a is useful as a stable and highly active catalyst for asymmetric hydrogenation of -N-acyl-dehydro-α-amino acids yielding, in 94 – 99% e.e., N-acyl-(S)-α-amino acids. Only slightly lower e.e.s are obtained for the corresponding esters. The rate of hydrogenation considerably increases with hydrogen pressure, this having practically no influence on the optical yield. A decrease of temperature leads to enhanced enantioselectivity, following the Eyring equation. Neutral complexes have only slight activity. The α-anomer did not show consistent and high e.e. Strong solvent effects are observed.