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?

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:

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: