Stereoselectivity chiral organolithium compounds

In general, nucleophilic addition reactions using Grignard or organolithium reagents to -chiral or other remotely chiral ketones usually yield mixtures of stereoisomers which are not synthetically use-fiil.9,12-27 However, some specific examples of stereoselective organolithium and Grignard additions to these remotely chiral carbonyl compounds have been reported. 

A chiral auxiliary is a chiral molecule attached to the starting material of the reaction dia-stereoselective reactions of compounds from the chiral pool are likewise controlled by chirality in the starting material, and we call this type of stereocontrol substrate control. But is it also possible for enantioselective reactions to be controlled by chiral reagents. For example, a typical achiral base will just remove a proton from a substrate, but an enantiomerically pure chiral base can select one of two enantiotopic protons and form a product enantioselectively. The product of course has to be chiral, so we can t use a chiral base to make planar enolates enantioselectively, for example, but we can a chiral base to make chiral organolithiums. 

Chiral ligand-mediated lithiation-substitution sequences to promote stereoselectivity in pro-chiral compounds have been exploited widely over the past decade25. An asymmetric deprotonation carried out by the organolithium can be the enantio-determining step, or an asymmetric substitution as a postdeprotonation step. (—)-Sparteine, a readily available alkaloid, has been extensively used in this type of stereoselective transformation, giving high yields of enantiomeric excess. 

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