Enantioselective carbometallation of alkenes

If an efficient method was available to render such a process asymmetric, it would acquire utility in the creation of asymmetric vicinal carbon atoms. However, until now, such enantioselective carbometallation reactions have been scarce because of the difficulty of enantiofacial differentiation of an unactivated alkene. Here we describe the more important results in this field. 

the kinetic resolution of a variety of pyrans [123] and cyclic allyl ethers (six-, seven- and eight-membered vinyl systems) was investigated [124]. In all cases, a very high enantioselectivity of the remaining starting materials was obtained. 

Recently, a novel C,-symmetric zirconocene dichloride CpCp ZrCl2 (Cp = C5H5, Cp = 1-neomenthyl-4,5,6,7-teuahydroindenyl) was prepared, in which the alkene can only approach from one side. With this chiral ligand, the ethylmagnesiation of unsubstituted allylic amines or alcohols leads to good enantioselectivities [125]. 

the two enantiomers of 92 can be synthesized from (—)sparteine by switching the stereochemistry of the double bond of cinnamyl alcohol from E to Z [128]. 

More recently, asymmetric intramolecular carbolithiation was described, either with a remote chiral center in a suitable position to promote a diastereofacial differentiation of the olefin [130] or with a chiral organolithium derivative [131]. In the former case, alkylation 

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