Question

Question: When both carbons ortho to the aryl oxygen are not bonded to hydrogen, an allyl aryl ether rearranges to a para-substituted phenol. Draw a stepwise mechanism for the following reaction, which contains two [3,3] sigmatropic rearrangements.

Short answer

Answer

Step-by-step solution

Sigmatropic rearrangement

These intramolecular reactions involve an exchange of a σ-bond with another σ-bond without the use of a catalyst.

[3,3] Sigmatropic reaction

The para-Claisen rearrangement involves the shift of an allyl aryl ether to the para position when both of the ortho positions are blocked.

Mechanism of the given reaction

On heating, the allyl group shifts to the ortho position, leading to an increase in steric density at the ortho position. The allyl group rearranges to move at para-position and on tautomerization gives the final product.