2-Methylenetetrahydropyrans: efficient partners in the carbonyl ene reaction.

The carbonyl ene reaction of 2-methylenetetrahydropyrans provides a rapid, high yielding route for the preparation of ß-hydroxydihydropyrans under mild conditions. This process provides a new entry for the synthesis of 2-substituted tetrahydropyrans and for the direct introduction of oxygen heterocycles into molecular frameworks.