Claisen rearrangement

What is Claisen Rearrangement?

(Claisen Rearrangement | Eschenmoser-Claisen Rearrangement | Ireland-Claisen Rearrangement | Johnson-Claisen Rearrangement | Overman Rearrangement).

The Claisen rearrangement is a chemical reaction that allows for the synthesis of compounds containing a double bond. This reaction is named after the German chemist Rainer Ludwig Claisen, who first described it in 1887. The Claisen rearrangement involves the rearrangement of a compound called an “allylic vinyl ether” to a compound containing a double bond. The reaction is typically carried out in the presence of a base, such as sodium ethoxide, and a solvent, such as ethanol..

Claisen rearrangement
Claisen Rearrangement

One of the advantages of the Claisen rearrangement is its high yield and efficiency. It is a relatively simple reaction that can be carried out under mild conditions and does not require the use of expensive or specialized reagents..

The Claisen rearrangement has a wide range of applications in the synthesis of pharmaceuticals, fragrances, and other chemicals. It has also been used in the synthesis of natural products, such as flavonoids and terpenoids..

Summary

The Claisen rearrangement is a valuable tool for the synthesis of compounds containing a double bond and has played an important role in the development of a number of important chemical compounds..

Example

One example of a Claisen rearrangement is the conversion of 3-penten-2-ol to 3-ethyl-2-penten-1-ol. The reaction can be represented by the following equation:

3-Penten-2-ol -> 3-Ethyl-2-penten-1-ol

The reaction occurs in the presence of a base, such as sodium ethoxide, and proceeds through the formation of an intermediate compound called an enolate ion, which then undergoes a nucleophilic attack on the alkene bond of the starting material to form the final product..

This reaction is an important synthetic tool in organic chemistry and is widely used in the preparation of a variety of compounds, including flavors, fragrances, and pharmaceuticals..

Mechanism of reaction

In the following reaction:

3-Penten-2-ol -> 3-Ethyl-2-penten-1-ol

the mechanism of the Claisen rearrangement can be divided into three main steps:

  • Formation of the enolate ion: The first step in the Claisen rearrangement is the formation of an enolate ion from the starting material, which is typically an allyl vinyl ether. This is typically achieved by reacting the allyl vinyl ether with a strong base, such as sodium ethoxide, to produce a nucleophilic enolate ion..
  • Nucleophilic attack: The enolate ion then undergoes a nucleophilic attack on the alkene bond of the starting material, which results in the formation of an intermediate compound known as a 1,2-alkyl shift intermediate..
  • Deprotonation: The 1,2-alkyl shift intermediate is then deprotonated by the base to form the final product, which is a substituted allylic alcohol. This step is accompanied by the release of a small molecule, such as water or methanol, which is produced by the abstraction of a proton from the base..

References

  • Claisen, L. (1912), Über Umlagerung von Phenol-allyläthern in C-Allyl-phenole. [On rearrangement of phenol-allyl ethers to C-allyl phenols.] Ber. Dtsch. Chem. Ges., 45: 3157-3166. https://doi.org/10.1002/cber.19120450348
  • Claisen, L. and Tietze, E. (1925), Über den Mechanismus der Umlagerung der Phenol-allyläther. [On the mechanism of rearrangement of phenol allyl ethers.] Ber. dtsch. Chem. Ges. A/B, 58: 275-281. https://doi.org/10.1002/cber.19250580207
  • Claisen, L. and Tietze, E. (1926), Über den Mechanismus der Umlagerung der Phenol-allyläther. (2. Mitteilung). [On the mechanism of rearrangement of phenol allyl ethers. (2. Communication).] Ber. dtsch. Chem. Ges. A/B, 59: 2344-2351. https://doi.org/10.1002/cber.19260590927
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