Claisen rearrangement

Claisen Rearrangement

The Claisen rearrangement is a powerful organic reaction that involves the rearrangement of allyl vinyl ethers to form β-keto esters or β-diketones. This reaction was first discovered by the German chemist Rainer Ludwig Claisen in 1912 and has since become an important tool in synthetic organic chemistry.

Mechanism

The Claisen rearrangement proceeds through a concerted pericyclic process known as a sigmatropic rearrangement. The reaction is initiated by the migration of an alkyl or aryl group from the oxygen atom to the carbon atom adjacent to the carbonyl group. This migration is accompanied by the formation of a new carbon-carbon bond and the breaking of the carbon-oxygen bond. The resulting intermediate then undergoes a tautomeric shift to form the final product.

Applications

The Claisen rearrangement has found numerous applications in organic synthesis. One of its most common uses is in the synthesis of β-keto esters, which are versatile building blocks in the production of pharmaceuticals and natural products. The reaction can also be used to synthesize β-diketones, which are important intermediates in the synthesis of complex organic molecules.

Variations

Several variations of the Claisen rearrangement have been developed to expand its synthetic utility. One such variation is the Johnson-Claisen rearrangement, which involves the rearrangement of allyl aryl ethers. Another variation is the Cope rearrangement, which involves the rearrangement of allyl vinyl ethers with a 1,5-diene moiety.

References

1. Claisen, L. (1912). "Ueber Umlagerung von Allylvinylethern in Allylphenylether". Justus Liebigs Annalen der Chemie. 394 (1): 1–53. doi:10.1002/jlac.19123940102.

2. Nicolaou, K. C.; Snyder, S. A.; Montagnon, T.; Vassilikogiannakis, G. (2002). "The Diels-Alder Reaction in Total Synthesis". Angewandte Chemie International Edition. 41 (10): 1668–1698. doi:10.1002/1521-3773(20020517)41:10<1668::AID-ANIE1668>3.0.CO;2-U.

See Also

• Pericyclic Reactions
• Organic Synthesis
• Beta-Keto Esters
• Diketones