| Abstract
| - A series of novel diphosphite ligands derived from readily available d-(+)-glucose have beensynthesized. These ligands were screened in the Rh-catalyzed hydrogenation of a series of α,β-unsaturated carboxylic acid derivatives. Both excellent enantioselectivities (ee up to >99%) andactivities were achieved. The advantage of these ligands is that their modular nature allows aneasy systematic variation in the configuration of the stereocenters (C-3, C-5) at the ligand backboneand in the biaryl substituents, so the optimum configuration for maximum enantioselectivity inasymmetric hydrogenation can be determined. Results show that enantiomeric excesses dependstrongly on the absolute configuration of C-3 and slightly on the stereocenter carbon C-5, whilethe sense of the enantiodiscrimination is predominantly controlled by the configuration of the biarylsat the phosphite moieties. Moreover, the presence of bulky substituents at the ortho-positions ofthe biaryl diphosphite moieties has a positive effect on enantioselectivity.
|
