Dienol-benzene rearrangement

What is dienol‐benzene rearrangement?

The dienol-benzene rearrangement is a chemical reaction that has its roots traced back to 1956. It involves the acid-promoted conversion of 4,4-disubstituted cyclohex-2,5-dienol into substituted benzene. The reaction proceeds via a transition state and intermediate, both of which exhibit substantial carbonium ion characteristics. Interestingly, the reaction is catalyzed solely by H+ in acetate, formate, and phosphate buffers. However, in aqueous solutions of HClO4 and H2SO4, the rearrangement exhibits first-order kinetics for 4-methyl-4-trichloromethyl cyclohex-2,5-dienol. On the other hand, the rearrangement of 4,4-dimethyl cyclohex-2,5-dienol is more complex, involving isomerization to 6,6-dimethylcyclohex-2,4-dienol, which yields o-xylene. This reaction finds utility in introducing aromaticity into the A-ring of steroids.

Dienol‐benzene rearrangement
Dienol‐benzene rearrangement

The driving force of these reactions is the aromatization. Also, the reaction media affects the rearrangement and the regioselectivity is controlled by the electronic factors.