Spiro- and Bicycloannulation of Sulfoximine-Substituted 2-Hydroxy-dihydropyrans: Enantioselective Synthesis of Spiroketals, Spiroethers, and Oxabicycles and Structure of Dihydropyran Oxocarbenium Ions
skeletons. These routes were extended to the synthesis of spiroketals and spiroethers incorporating additional annulated six-membered rings. Diastereoselective Prinscyclization of mono- and bicyclic 2-alkenyl-2-hydroxy-dihydropyrans was highly selective and afforded chloro-substituted spirocycles. Substituted 2-hydroxy-dihydropyrans were obtained through cyclization of δ-hydroxy ketones, which were synthesized