Question

The following reaction involves a starting material with a double bond and a hydroxyl group, yet its mechanism resembles a pinacol rearrangement. Propose a mechanism, and point out the part of your mechanism that resembles a pinacol rearrangement.

Short answer

Diols can be transformed into cyclic ethers using an acid catalyst. This process is termed diol cyclization. The breakage of the C-C bond in vicinal diol generates a ketone or aldehyde.

Step-by-step solution

Reactions of diols

Diols can be transformed into cyclic ethers using an acid catalyst. This process is termed diol cyclization. The breakage of the C-C bond in vicinal diol generates a ketone or aldehyde.

Pinacol rearrangement

Pinacol rearrangement constitutes dehydration reactions that result in the generation of a pinacolone. This rearrangement reaction is frequently used in acid-catalyzed diol reactions.

Pointing out the part of the mechanism that resembles a pinacol rearrangement

In pinacol rearrangement, the first step is the hydroxyl group protonation, and second is the methyl group migration. The third step is the deprotonation to generate the product. The migration of the methyl group and the deprotonation steps resemble the pinacol rearrangement.

The mechanism of the reaction can be given as:

The mechanism that resembles the pinacol rearrangement