Dienone–phenol rearrangement

Reaction mechanism

The reaction mechanism of 4,4-disubstituted cyclohexadienones to 3,4-disubstituted phenol is illustrated here.

The migration tendency for the two different groups (R) present at either 4,4 position or 2,2 position can be determined by comparing the relative stability of the intermediate carbocation formed during rearrangement. In case of acid-promoted conditions, some relative migration tendencies are: COOEt > phenyl (or alkyl); phenyl > methyl; vinyl > methyl; methyl > alkoxy and alkoxy > phenyl. In some cases such as allyl and benzyl group, the actual rearrangement might happen through the Cope rearrangement. Apart from acid catalysis, the dienone–phenol rearrangement is also possible in presence of base. The dienone–phenol rearrangement has been used in the synthesis of steroids, anthracenes, and phenanthrenes.