Chiral Mono- and Bidentate Ligands Derived from D-Mannitol and Their Application in Rhodium(I)-Catalyzed Asymmetric Hydrogenation Reaction

摘要

The new monodentate phosphoramidites 8a-g and bidentate phospholanes 13a-e are prepared in an ex-chiral-pool synthesis from D-mannitol. Chiral diols 7a-g, obtained via nucle-ophilic ring opening of bis(epoxides) 6a-b, are the key inter-mediates for the production of both classes of ligands. Treatment of 8a-g or 13a-e with [PdCl_2(COD)] or [Rh(COD)_2][-SO_3CF_3] yield the corresponding Pd (10a, 10f, 15a) and Rh compounds (9a-g and 14a-e), respectively. The C_2 symmetry of the comlexes in the solid state is demonstrated by X-ray structure investigations performed on 10a, 10f and 15a. Sur-prisingly high enantioselectivities in the asymmetric hydro-genation of itaconic acid (94% ee) and alpha-acetamidocinnamic acid (89% ee) are observed on using the Rh complex 9g bearing two monodentate phosphoramidite ligands. Although the chelating bis(phospholanes) described heriein are more effective, the adjustable synthesis of the monodentate phos-phoramidites my permit the optimization of asymmetric catalytic reactions.