The Claisen rearrangement, named after Ludwig Claisen, is a pericyclic rearrangement, the course of which is analogous to that of the Cope rearrangement.
It proceeds through a six-membered transition state with two π bonds and one σ bond. The Claisen rearrangement is also referred to as the Oxa-Cope rearrangement and is assigned to the sigmatropic reactions in which a σ-bond, which is adjacent to one or more π-electron systems, migrates to a new position in a [3,3] -shift.
An allyl vinyl ether reacts in this way to form a γ, δ-unsaturated carbonyl compound. Since allyl phenyl ethers also convert accordingly, a distinction is made between the aliphatic and the aromatic Claisen rearrangement.
Both the aliphatic and the aromatic Claisen rearrangement are in many cases thermal isomerizations, temperatures> 100 make necessary. By using Lewis acid catalysts, in particular transition metal complexes, these reactions can be carried out under mild conditions.