Asymmetric Hydrosilylation by Means of Homogeneous Catalysts with Chiral Ligands

Abstract

Asymmetric synthesis has acquired much interest for a long time, and many types of stoichiometric reactions have been explored [1]. However, the most effective use of chiral reagents is their use as catalysts. Stereoselective reactions catalyzed by chiral transition metal complexes may be of great promise. In general, an attractive approach to ‘homogeneously catalyzed asymmetric reactions’ has been made possible mainly by the development of preparative routes to optically active phosphines as ligands. Yet, one of the crucial problems is how to develop a chiral ligand which will enable the catalyst for a particular reaction to be as efficient in stereoselectivity as possible. At the present time the choice of the chiral ligand for this purpose is quite empirical. In this sense, some of the most exciting developments in asymmetric synthesis have been made on the catalytic asymmetric hydrogenation of prochiral olefins using soluble rhodium(I) complexes with chiral phosphine ligands. Knowles et al. [2] have found that the catalytic hydrogenation of α-acylamidocinnamic acids affords the corresponding amino acid derivatives with 80–95 percent enantiomeric excess (% e.e.) using rhodium complexes with (R)-o-anisylcyclohexylmethylphosphine or (R)-bis(o-anisylphenylphosphino)ethane. Similar results have been obtained by Kagan and Dang [3] by the use of a rhodium catalyst with (—)-2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane (DIOP) as ligand.KeywordsAsymmetric SynthesisOptical YieldRhodium ComplexAsymmetric ReductionProchiral KetoneThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.