Claisen condensation



The Claisen condensation (not to be confused with the Rainer Ludwig Claisen, who first published his work on the reaction in 1881.

Requirements

At least one of the reagents must be enolizable (have an types of Claisen condensations.

The base used must not interfere with the reaction by undergoing lithium diisopropylamide, or LDA, may be used, since only one compound is enolizable. LDA cannot be used in the classic Claisen or Dieckmann condensations, since virtually all ester will be converted to ester enolate and condensation will not occur.

The alkoxy portion of the ester must be a good Methyl and ethyl esters, which yield the methoxy and ethoxy leaving groups, respectively, are usually used.

Types


The classic Claisen condensation, where only one enolizable ester is used.


The mixed (or "crossed") Claisen condensation, where an enolizable ester or ketone and a nonenolizable ester are used.


The cyclic β-keto ester. In this case, the ring formed must not be strained, usually a 5- or 6-membered ring.

Mechanism

In the first step, the ester with the α-proton is deprotonated by the base, resulting in the enolate anion, made relatively stable by the neutralize the base and any enolate still present. The newly-formed β-keto ester or β-diketone is then isolated.

See also

References

  • Carey, Francis A. (2006). Organic Chemistry, Sixth Edition, New York, NY: McGraw-Hill. ISBN 0-07-111562-5. 
  • Claisen, L., and A. Claparede. Ber. Deut. Chem. Ges., 1887, 14, 2460.
  • Claisen, L. Ber. Deut. Chem. Ges., 1887, 20, 655.
 
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