Question

In the following reaction 'B' is

• A.
• B.
• C.
• D.

Answer 1

The Correct Option is D

Acid-Catalyzed Cyclization Mechanism

The given reaction is an acid-catalyzed intramolecular cyclization of an unsaturated alcohol. The mechanism involves:

1. Protonation of the alcohol: The hydroxyl group is protonated by \(\text{H}_3\text{O}^+\), making it a better leaving group.
2. Carbocation formation: Water leaves, generating a secondary carbocation.
3. Cyclization: The double bond attacks the carbocation, forming a six-membered ring. This results in a tertiary carbocation. Crucially, this carbocation is formed adjacent to the oxygen in the newly formed ring.
4. Deprotonation: A proton is lost to give the final cyclic ether product.
   

The correct product, resulting from the more stable tertiary carbocation and forming the six-membered ring, is option (4).