Pericyclic Reactions
In organic chemistry, a pericyclic reaction is a concerted reaction whose transition state has a cyclic geometry. These reactions are complex, but they can be used to prepare carbonyl compounds.
Claisen rearrangement
It takes place from suitable allyl vinyl or allyl aryl ethers. A vinyl ether can be easily prepared by Markovnikov addition of an alcohol to an alkyne.
It looks like magic, doesn't it? It takes place through a reorganization of the π clouds and the breaking and formation of σ bonds around them.
Doesn't it remind you of the Diels-Alder reaction, but in an intramolecular version?
The reaction is named after Ludwig Claisen.
Oxy-Cope rearrangement
If the C=C double bonds are in the appropriate position relative to an alcohol, the pericyclic reaction can give an enol, which immediately equilibrates with the corresponding keto form.
The Cope rearrangement is named after Arthur C. Cope.