Recent Advances in Metal-Catalyzed Asymmetric Conjugate Additions

Abstract

The conjugate addition of carbon nucleophiles to acceptor activated olefins is one of the most important reactions for carbon-carbon bond formation. With optically active metal complexes this transformation can be catalyzed enantioselectively. This review is a collection of the newer literature (since 2001) on this topic. The metal salts and complexes applied are in a broad range, starting from solely Lewis acidic M(II) and M(III) compounds, such as magnesium, zinc, boron, aluminum and the lanthanoids. Transition-metal catalysts suitable for asymmetric conjugate additions are compounds of ruthenium, iridium, nickel, and palladium. The most flourishing fields are, however, the catalysis with rhodium and copper complexes. Rhodium catalysts often have a chiral diphosphane like BINAP, or an optically active olefin as the ligand, the latter being a newer development. The privileged ligand structures for copper catalysts are monodentate phosphoramidites with axially chiral BINOL or other biphenol units.