Single stereodifferentiation associated with carbon atom insertion during the oxonium ion-initiated pinacol rearrangement of dihydrofuranyl and dihydropyranyl carbinols

摘要

The stereoselectivity of the acid-promoted rearrangement of dihydrofuranyl and dihydropyranyl carbinols to spirocyclic ketones has been examined. These kinetically controlled isomerizations result in the ring expansion of the hydroxyl-substituted ring with generation of a newly stereogenic spirocyclic carbon atom. All of the adducts formed from several 4,5-dihydorfurans and cyclo- butanone, cyclopentanone, and 2,2-dimethylcyclopentanone proved to be reactive.