Lewis acids ligand

Entry Lewis acid Ligand 798 time/days Yield (%)° ee (%) ... 

In 2000, a catalytic enantioselective addition was reported using a chiral Lewis acid-ligand system. Tomioka and coworkers reported the enantioselective addition of... 

The five coordinate Beat complex (4) has both a vacant coordination site and a labile chloride ligand. As shown in Scheme 3 addition of a simple Lewis acid ligand affords the saturated complexes (8) or (9) where the introduced ligand is tram to Beat.4 Halide removal from (4) with AgSbFJMeCN gives the cation (10) in which the two acetonitrile ligands can be easily... 

The relative stereochemistry of the major adducts is assigned to be syn, and the predominant re face-attack of enol ethers at the aldehyde carbonyl carbon has been confirmed when a natural tartaric acid derivative is used as a Lewis acid ligand. The use of an unnatural form of tartaric acid as a chiral source gives the other enantiomer, as expected. Almost perfect asymmetric induction are achieved with the syn adducts. 

A prochiral radical intermediate is generated from a-methoxymethyl-a-iododihy-drocoumarin (la) which is coordinated via the carbonyl oxygen to the chiral Lewis acid/ligand combination of MgL and 2. Enantiomeric excesses of up to 62% and yields of 88% have been obtained in this enantioselective reduction using tributyltin... 

Use of various a-type (Lewis base) and p-type (Lewis acid) ligands that can form complexes with the counterion or with the propagating ion pair. This can lead to faster aggregation dynamics of the ligand-complexed ion pairs. 

On the basis of a study of time-dependence of the molecular weight of the Lewis acid, ligand (144) forms a monomer with i-Bu2AlCl immediately after the reaction, which is converted to a dimmer after 20 hours and further to high molecular weight aggregates after 120 hours. 

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