Write a mechanism that explains the formation of the following product. In your mechanism, explain the cause of the rearrangement, and explain the failure to form the Zaitsev product.

Bridge head carbocation is formed at bridge head carbon and is unstable, as Bret's rule states that bridge head carbons cannot form double bonds. This is due to drastic angle strain which can result in atoms being out of the plane. As carbocation is planar, bridge head carbon cannot be a carbocation.

Given reactant undergoes proton abstraction in the first step, and oxygen of hydroxyl abstracts proton from the acid and gets converted into the good leaving group. It is followed by the formation of a carbocation. This carbocation undergoes a bond shift and forms stable tertiary carbocation. Formation of Zaitsev product is not possible as bridge head carbon cannot be planar and formation of double bond induces planarity, thus product from tertiary carbocation is not possible.

Hence, the tertiary carbocation formed undergoes a hydride shift to form secondary carbocation, as the formation of alkene from this carbocation will not disturb the planarity of the molecule. Thus, a major product is formed from secondary carbocation.

Formation of product from secondary carbocation