Asymmetric synthesis magnesium enolates

Asymmetric synthesis in aldol-type reaction involving magnesium ester or lactone enolates has also been reported. Enolate of (—)-menthyl or (-l-)-bornyl acetate reacts with substituted benzophenones or a-naphtophenones to yield, upon hydrolysis of the resulting esters, optically active /3-hydroxyacids. Although these results are interpreted in terms of a steric factor. Prelog s rules are not applicable to these reactions (equation 88). 

The chemistry of magnesium bisamides has been reviewed" . They can be used for the regio- and stereoselective formation of enolates", while chiral magnesium amides are applied in asymmetric synthesis for enantioselective enolisations ". 

The chemistry of magnesium bis-amides has been reviewed.21 Magnesium bis-amides have been used for the region- and stereoselective formation of enolates.2 a Enantioselective enolization with chiral magnesium amides has been applied in asymmetric synthesis.23 233... 

Silyl enol ethers react with aldehydes in the presence of chiral boranes or other additives " to give aldols with good asymmetric induction (see the Mukaiyama aldol reaction in 16-35). Chiral boron enolates have been used. Since both new stereogenic centers are formed enantioselectively, this kind of process is called double asymmetric synthesis Where both the enolate derivative and substrate were achiral, carrying out the reaction in the presence of an optically active boron compound ° or a diamine coordinated with a tin compound ° gives the aldol product with excellent enantioselectivity for one stereoisomer. Formation of the magnesium enolate anion of a chiral amide, adds to aldehydes to give the alcohol enantioselectively. 

The reactions of aldehydes with enolates of acetic esters (MeCOOG ) 1.18 (R = H) are often poorly selective [66, 147, 209, 408, 1186, 1258], For this reason, the asymmetric synthesis of acetate aldols is usually performed by reduction of a-bromo analogs with BU3S11H [1254] or from sulfoxides [1049] (see below). However, the reactions of lithium or magnesium enolates of monoacetates of (hols... 

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