ChemInform Abstract: Bis(phospholane) Ligands Containing Chiral Backbones. Matching and Mismatching Effects in Enantioselective Hydrogenation of α-Keto Esters.
Abstract
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ChemInform Abstract
The synthesis of several novel bis(phospholane) ligands containing a chiral 2,4-pentylene backbone, e.g. SBDPP and RBDPP, is described. Their utility is studied in the hydrogenation of α-aminocarboxylic esters like (I) and of α-keto ester (III) in the presence of a [Rh(cod)(ligand)]OTf catalyst. It is shown, that the sense of stereoinduction is determined by the phospholane stereochemistry of the ligand, since reduction products of the same configuration are obtained irrespective of the configuration of the ligand backbone. In contrast, the degree of stereoinduction strongly depends on the nature of ligand backbone. The best results are obtained for ligand SBDPP (75% e.e.), while with diastereomeric ligand (RBDPP) as well as the parent compound (BDPPR) the reduction products are obtained in only low optical purity.
