Enantioselective Michael addition of a chiral organometallic reagent to a prochiral substrate is an attractive method for creating a center of chirality in an organic molecule. [1] For this purpose chirally modified organocopper compounds of composition RCu(L*)Li can be used; the chiral nontransferable ligand L* controls the stereochemical course of the transfer of group R to the substrate 1. By using stoichiometric amounts of these Βͺchiral cupratesΒΊ, the groups of Bertz, Corey, Dieter, Rossiter, and Tanaka obtained the 1,4-adducts 2 with good
enantioselectivities (over 90 % ee in some cases). Naturally occuring alcohols and amines were used as chiral ligands L* (e.g., ephedrine and proline derivatives). [1] However, these investigations also revealed two fundamental problems of enantioselective Michael additions: 1) In solution organocopper compounds show dynamic behavior with equilibria between several species. If this leads to the formation of achiral, but more reactive cuprates, a loss of enantioselectivity is unavoidable. Therefore, it is crucial to develop chiral reagents which react so rapidly with the substrate that undesired competing reactions are suppressed. 2) Many chiral organocopper reagents exhibit high substrate specificity; that is, they give good stereoselectivities with only one or very few Michael acceptors. Both problems may be solved by taking advantage of the concept of ligand-accelerated catalysis, [2] which involves catalytic reactions characterized by dynamic ligand-exchange processes. The presence of a suitable ligand can lead to the formation of a highly reactive and selective catalyst by selfassembly. If a chiral ligand is used, a stereoselective reaction may be favored over a nonselective one. Other advantages of