Asymmetric synthesis of spiroketal, spiroether, and oxabicycle building blocks via stereoselective spiro- and bicycloannulation of 2-hydroxy dihydropyrans.

A modular asymmetric synthesis of spiroketal, spiroether, and oxabicycle building blocks is described based on the spiro- and bicycloannulation of alpha-hydroxy dihydropyrans, which were obtained from sulfoximine-substituted homoallylic alcohols. Key steps of the syntheses are stereoselective Ferrier-type O- and C-glycosidation, ring-closing metathesis, and stereoselective Prins cyclization.