Organic reaction

Claisen Rearrangement

Scheme of the Claisen rearrangement.

The Claisen rearrangement is a fundamental organic reaction that involves the [3,3]-sigmatropic rearrangement of an allyl vinyl ether to produce a _,_-unsaturated carbonyl compound. This reaction is named after the German chemist Ludwig Claisen, who first reported it in 1912.

Mechanism

The Claisen rearrangement is a concerted process, meaning that it occurs in a single step without the formation of intermediates. The reaction proceeds through a six-membered cyclic transition state, which is a hallmark of pericyclic reactions. The driving force for the rearrangement is the formation of a more stable carbonyl compound from the less stable allyl vinyl ether.

Variants

Several variants of the Claisen rearrangement exist, including:

• The Johnson–Claisen rearrangement, which involves the use of an orthoester to generate the allyl vinyl ether in situ.
• The Ireland–Claisen rearrangement, which uses a silyl ketene acetal as the starting material and is performed under basic conditions.
• The Eschenmoser–Claisen rearrangement, which involves the rearrangement of allylic amines.

Applications

The Claisen rearrangement is widely used in organic synthesis to form carbon-carbon bonds and to introduce functional groups into molecules. It is particularly useful in the synthesis of natural products and complex organic molecules.

Related Pages

• Pericyclic reaction
• Sigmatropic reaction
• Cope rearrangement