Metal-Catalyzed Cycloetherification Reactions of beta,gamma- and gamma,delta-Allendiols: Chemo-, Regio-, and Stereocontrol in the Synthesis of Oxacycles

Versatile routes that lead to a variety of functionalized enantiopure tetrahydrofurans, dihydropyrans, and tetrahydrooxepines are based on chemo, regio, and stereocontrolled metal catalyzed oxycyclization reactions of beta,gamma and gamma,delta-allendiols, which were readily prepared from (R) 2,3-O-isopropylideneglyceraldehyde The application of Pd-II, Pt-II, Au-III, or La-III salts as the catalysts gives controlled access to differently sued oxacycles in enantiopure form Usually, chemoselective cyclization reactions occurred exclusively by attack of the secondary hydroxy group (except for the oxybromination of phenyl beta,gamma-allenic chols 3b and 3d) to an allenic carbon atom Regio- and stereocontrol issues are mainly influenced by the nature of the metal catalysts and substituents