Chapter 21: Ester Enolates

Summary

• Ketone enolates can be acylated with non-enolisable esters (i.e. an ester that lacks a-hydrogens).
• Reagents : most commonly the base would be the alkoxide, RO^-, matching the alcohol portion of the ester (why ?)
• Remember enolates are good nucleophiles and the ester carbonyl C are electrophilic, and undergo nucleophilic acyl substitution.
• There are two principle variations of this reaction:
• with a carbonate, such as diethyl carbonate, to give a b-ketoester
• with an ester to give a 1,3-diketone
• Note that the products of these reactions are b-dicarbonyls which are important, useful synthetic intermediates

	Acylation using diethyl carbonate
	Acylation using an ester

As an example, consider the reaction of acetone with diethyl carbonate, which gives ethyl acetoacetate:
Try to identify the enolate portion and the carbonyl portion in the different representations

• How else would you make ethyl acetoacetate using a condensation type reaction ? ANSWER

The intramolecular variation of this reaction is also possible when forming the favourable 5- or 6- membered rings, giving a cyclic 1,3-diketone product:

Intramolecular variation

• As an example, consider the following reaction which gives the cyclopentane system rather than the less favourable cycloheptane.
• This is similar to an intramolecular Aldol condensation or the Dieckmann condensation

• Claisen Condensation
• Other reactions of Ketone Enolates

© Dr. Ian Hunt, Department of Chemistry