Acyloin condensation
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Acyloin condensation is a reductive coupling of two carboxylic esters using metallic sodium to yield an α-hydroxyketone, also known as an acyloin.
The reaction is most successful when R is aliphatic and inert. To achieve the condensation, chemists should employ aprotic solvents with a high boiling point, such as benzene and toluene. (Usage of protic solvents results in the Bouveault-Blanc reduction.) Depending on ring size and steric properties, but independent from high dilution, the acyloin condensation of diesters favours intramolecular cyclisation over intermolecular polymerisation.
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[edit] Variations
[edit] Rühlmann-method
The method according to Rühlmann employs trimethylchlorosilane as a trapping reagent; by this, competing reactions are efficiently subdued. Generally, yields increase considerably. The hydrolytic cleavage of the silylether gives the acyloin. To achieve a mild cleavage methanol can be used in several cases.
Usually toluene, dioxane, tetrahydrofuran or acyclic dialkylethers are employed as solvents. Advantageously also N-methyl-morpholine has been used. It allowed in some cases a successful reaction, in which otherwise the reaction failed in less polar media.
[edit] References
- ^ Bouveault, L., and R. Loquin. Comptes. Rendus. 1905, 140, 1593.
- ^ Finley, K. T. Chem. Rev. 1964, 64, 573. (Review)
- ^ Rühlmann K., Synthesis, 1971, 236–253. (Review)
