Chiral NHC Ligands Research Articles

A Highly Active Chiral Ruthenium-Based Catalyst for Enantioselective Olefin Metathesis

A chiral Ru-based olefin metathesis catalyst bearing a chiral NHC ligand that is both C1-symmetric and monodentate is described. The catalyst shows increased reactivity in comparison to existing chiral Ru-based catalysts that possess a C2-symmetric NHC and successfully induces asymmetry in desymmetrization reactions.

Asymmetric Conjugate Addition of Grignard Reagents to Enones

The authors reported one of the first successful examples of enantioselective addition to trisubstituted enones. Such addition allows a simple creation of chiral quaternary centers, often difficult to form. This method is especially interesting, as it uses still uncommon chiral NHC ligands for copper in conjunction with Grignard reagents to achieve sufficient addition rates and stereo­control. Even unreactive enones like isophorone can be used in this reaction. Although so far the reported cases are limited to cyclohexanone derivatives, the used synthetic approach is very promising for further developments.

Bidentate NHC‐Based Chiral Ligands for Efficient Cu‐Catalyzed Enantioselective Allylic Alkylations: Structure and Activity of an Air‐Stable Chiral Cu Complex.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Bidentate NHC-based chiral ligands for efficient Cu-catalyzed enantioselective allylic alkylations: structure and activity of an air-stable chiral Cu complex.

Cu-catalyzed addition of alkylzinc reagents to a range of allylic phosphates is promoted efficiently and with high enantioselectivity to afford tertiary as well as quaternary carbon centers (up to 98% ee). Reactions proceed to completion with 0.5-5 mol % catalyst loading and are best promoted by commercially available CuCl2.2H2O. The X-ray structure of the chiral NHC-Ag(I) complex used in the study as well as that of a catalytically active NHC-Cu(II) complex are also reported; both complexes are air-stable and are formed in >/=95% isolated yield. The isolated Cu complex, which can be handled in air, is catalytically active. The present report provides the first precedent for efficient Cu-catalyzed allylic alkylations with chiral NHC ligands.