Claisen Condensation Reactions

• Claisen condensation is the self-condensation of esters.
• Below is an example of the claisen condensation of ethyl acetate to ethyl acetoacetate

• All steps are reversible except the last step, which drives the reaction to completion
• This diagram shows the conversion of an ester containing an alpha hydrogen into a beta-ketoester.
• The Alkoxide used as the base must be the same as the alcohol part of the ester in order to prevent the production of mixtures, through ester interchange.
• Alpha substituted esters cannot be used because the final proton transfer step cannot occur under normal reaction conditions. For example _______ cannot be used becasue it does not contain any aplha hydrogens.

• This can be overcome by using a strong base, such as triphenylmethylsodium.
• The mechanism of the claisen condensation reaction is similar to that of the aldol condensation reaction. It involves the nucleophilic acyl substitution of an ester enolate ion on the carbonyl of a second ester molecule.

Intramoleular Claisen Condensations

Mixed_Claisen_Reaction

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