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Crossed Claisen Condensation

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  • Crossed Claisen condensation is a variation of Claisen condensation.

    Claisen Condensation:



    Crossed Claisen Condensation:






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



    Step 2 and 3:  Enolate ion 1 undergoes a nucleophilic acyl substitution preferentially with the non-enolizable ester, which has the sterically less hindered and, therefore, more accessible carbonyl carbon, giving a  β-ketoester.



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



    Step 5:  The acid protonates enolate ion 2



    see also Dieckmann condensation