Chiral ligands addition with

Asymmetric addition of phosphonate [RCH2PO(OEt)2] to 4-substituted cyclohexanones has been promoted by chiral ligand additives with preferential formation of the Z-diastereoisomer in high enantiomeric excess. ... 

Zhang and Chan122 found that Hg-BINOL, (R)- or (S )-134, in which the naphthyl rings in the BINOL were partially hydrogenated,123 can give even better results in the diethylzinc reactions. Using (R)- or (5,)-134 as the chiral ligand, addition of diethylzinc to aromatic aldehydes proceeds smoothly with over 95% ee and, in most cases, quantitative conversion.122... 

SCHEME 2. Asymmetric conjugate addition of organolithium reagents with stoichiometric chiral ligands. Adapted with permission from Acc. Chem. Res., 40, 179-188 (2007). Copyright 2007 American Chemical Society... 

There are several examples of the effect of LiX on enolate aggregation leading to increased enantiomeric excess in asymmetric chemical events. Koga and co-workers developed an efficient enantioselective benzylation of the lithium enolate of 19 by using a stoichiometric amount of chiral ligand 22 with LiBr in toluene [50]. The chiral lithium amide 22 was prepared by treatment of a mixture of the corresponding amine 21 and LiBr in toluene with a solution of n-BuLi in hexane. Sequential addition of ketone 19 and benzyl bromide gave rise to 20 in 89 % yield and 92 % ee. The amount... 

Another important reaction associated with the name of Sharpless is the so-called Sharpless dihydroxylation i.e. the asymmetric dihydroxylation of alkenes upon treatment with osmium tetroxide in the presence of a cinchona alkaloid, such as dihydroquinine, dihydroquinidine or derivatives thereof, as the chiral ligand. This reaction is of wide applicability for the enantioselective dihydroxylation of alkenes, since it does not require additional functional groups in the substrate molecule ... 

Table 5. Conjugate Addition to Acyclic Enones with External Chiral Ligands O, O...

Abstract The dirhodium(II) core is a template onto which both achiral and chiral ligands are placed so that four exist in a paddle wheel fashion around the core. The resulting structures are effective electrophilic catalysts for diazo decomposition in reactions that involve metal carbene intermediates. High selectivities are achieved in transformations ranging from addition to insertion and association. The syntheses of natural products and compounds of biological interest have employed these catalysts and methods with increasing frequency. 

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