Claisen Condensation

21 October, 2014 / by SK / in Reactions

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General Characteristics

The base-promoted condensation of esters is called the Claisen condensation. The crossed-Claisen condensation between two different esters is effective if one of the esters does not have any α-hydrogens. The intramolecular Claisen condensation is particularly referred to as the Dieckmann reaction.

General References

・Claisen, L.; Claparede, A. Ber. 1887, 14, 2460.
・Claisen, L.; Lowman, O. Ber. 1887, 20, 651.
・Hauser, C. R.; Hudson, B. E. Org. React. 1942, 1, 266.
・Bartmess. J. E.; Hays, R. L.; Caldwell, G. J. Am. Chem. Soc. 1981, 103, 1338. DOI: 10.1021/ja00396a006

Reaction Mechanism

All steps of the reaction are reversible, but the equilibrium is shifted towards the product side because the eliminated alkoxide deprotonates the highly acidic proton of the β-ketoester product. For the same reason, more than one equivalent of base is required unlike aldol reactions. α,α-Disubstituted esters, for which the reaction cannot be promoted by the deprotonation of the product, tend to be sluggish substrates.