Prostereogenic enolates enantioselective protonation

Eames, J. Weerasooriya, N. Recent Avances into the Enantioselective Protonation of Prostereogenic Enol Derivatives, Tetrahedron Asymmetry 2001,12,1-24. 

Several methodologies have been developed to generate the prostereogenic intermediate necessary to achieve enantioselective protonation but all have in common a stable or transient species, enol or enolate, which is being protonated by a chiral proton source. In specific cases, it is difficult to determine the real structure of the intermediate obtained, enolate or enol or both, because of the lack of its characterization and precise mechanistic investigations. 

Proton transfer. Protonation of prostereogenic enolates with the y-hydroxyselenoxides, such as 1, sometimes gives excellent ee. The SnCl complex of a methyl ether of chiral BINOL can be used in catalytic amounts to protonate silyl enol ethers, affording ketones in high optical yields. A catalytic enantioselective deprotonation to form a bromoalkene is achieved by KH in the presence of A-methylephedrine. 

Fames J, Weerasooriya N. Recent advances into the enantioselective protonation of prostereogenic enol derivatives. Tetrahedron Asymm. 2001 12 1-24. 

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