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Alkali metal (especially Na, K) enolates can undergo conjugate addition

المؤلف:  Jonathan Clayden , Nick Greeves , Stuart Warren

المصدر:  ORGANIC CHEMISTRY

الجزء والصفحة:  ص597

2025-06-28

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The use of two anion-stabilizing groups is a sure way of promoting conjugate addition, but it not essential. Simple lithium enolates are not ideal nucleophiles for thermodynamically controlled conjugate addition because lithium binds strongly to oxygen and so tends to stabilize the aldol product. Better results are often observed with sodium or potassium enolates, which are more dissociated. Potassium tert-butoxide is the ideal base for this example as it is hindered and so will not attack the ester but is basic enough to deprotonate the ketone to a certain extent. Two enolates are possible but, under the equilibrating conditions, the more stable enolate is the one leading to the product with a quaternary carbon atom.

If the enolate carries a leaving group, we get a nice way of making a cyclopropane because the enolate formed by the conjugate addition can itself be alkylated.