Effect of ortho substituents on the direction of 1,2-migrations in the rearrangement of 2-exo-arylfenchyl alcohols

Ortho substituents on the aryl ring do not favor the Wagner-Meerwein rearrangement, as evidenced by adverse steric and electronic effects such as weaker resonance stabilization of the carbocation and steric encumbrance to nucleophilic attack. When the ortho substituent itself is nucleophilic, the barrier to Wagner-Meerwein rearrangement is overcome. This may be due to internal trapping of the carbocation to the exo side to yield a reactive intermediate that is predisposed to concerted bond migration. This was found in a study of the effect of ortho substituents on 1,2 migrations in 2-exo-arylfenchyl alcohols.