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Claisen Condensation

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    39362
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    Claisen condensation, not to be confused with Claisen rearrangement, is the reaction of an enolizable ester with a strong base to give a β-ketoester.

    claisencondensation1.png

    The most commonly used strong base in organic reactions, hydroxide ion, is not suitable for Claisen condensation because it could cause saponification of the ester. The base of choice in Claisen condensation is the alkoxide ion corresponding to the alkoxy group in the ester. Other alkoxides could cause transesterification of the ester. Since the β-ketoester formed in Claisen condensation is converted to the corresponding enolate ion by the base, in order to isolate the β-ketoester, when the reaction is complete, the reaction mixture needs to be acidified.

    eg:

    claisencondensation2.png

    Mechanism

    Step 1: The alkoxide ion deprotonates the enolizable ester reversibly.


    claisencondensation3.png

    Step 2 and 3: Enolate ion 1 undergoes a nucleophilic acyl substitution with the unreacted ester to give the β-ketoester.

    claisencondensation4.png

    Step 4: The alkoxide ion deprotonates the β-ketoester irreversibly.

    claisencondensation5.png

    Step 5: The acid protonates enolate ion 2.

    claisencondensation6.png

    see also Dieckmann condensation


    This page titled Claisen Condensation is shared under a All Rights Reserved (used with permission) license and was authored, remixed, and/or curated by Gamini Gunawardena via source content that was edited to the style and standards of the LibreTexts platform.

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