Ketone, 1-adamantyl ethyl aldol reaction

E -Enolates often react with lower stereoselectivity than those of the corresponding Z-enolates. A classic example to illustrate this point is a study carried out by Heathcock et al.6 (Scheme 2.IV). When the carbonyl compounds 1 were deprotonated with lithium diisopropylamide (LDA) and the resulting enolates were subsequently treated with benzaldehyde at -72° C, the aldol products desired (2) were obtained in 83 to 99% yield. The Z-enolates derived from t -butyl and 1-adamantyl ethyl ketones afforded syn -products in excellent levels of diastereoselectivity. The fact that the syn/anti ratios directly reflect the isomeric purity of the reacting enolates hints that the Z-enolates in these cases undergo aldol reaction through a chairlike six-membered transition state (Scheme 2.III,... 

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