Question

a. Draw the product of the following reaction:

b. If the terminal sp² carbon of the substituent attached to the benzene ring is labeled with 14C, where will the label be in the product?

Short answer

The given reactant is the allyl vinyl ether; it will undergo Claisen rearrangement, a [3,3] sigmatropic rearrangement (involving three pairs of electrons),and forming a six-membered ring transition state. The reactions, therefore, must be able to take place by asuprafacial pathway.

Because [3,3] sigmatropic rearrangements involve three pairs of electrons, they occur by a suprafacial pathway under thermal conditions. The product is formed by breaking the sigma bond between the oxygen and carbon and joining the two fragments at the 3^rd carbon form a keto form, which tautomerize to form the more stable enol form as the product is shown as follows:

Step-by-step solution

 Step 1: Product of Given reaction

The given reactant is the allyl vinyl ether; it will undergo Claisen rearrangement, a [3,3] sigmatropic rearrangement (involving three pairs of electrons),and forming a six-membered ring transition state. The reactions, therefore, must be able to take place by asuprafacial pathway.

Because [3,3] sigmatropic rearrangements involve three pairs of electrons, they occur by a suprafacial pathway under thermal conditions. The product is formed by breaking the sigma bond between the oxygen and carbon and joining the two fragments at the 3^rd carbon form a keto form, which tautomerize to form the more stable enol form as the product is shown as follows:

Labeled Product

The given reaction is [3,3] sigmatropic rearrangement; the terminal carbon of the substituent attached to the benzene ring is labeled with 14C, which is the 3^rd carbon from the one fragment formed by the breaking of the carbon-oxygen sigma bond.

The product is formed by joining the 3^rd carbon of both the fragment formed by breaking a carbon-oxygen sigma bond and the labeled carbon that appears in the product is shown as follows: