Organocatalytic Enantioselective Cycloetherifications Using a Cooperative Cation-Binding Catalyst

A highly enantioselective cycloetherification strategy for the straightforward synthesis of enantioenriched tetrahydrofurans, tetrahydropyrans, and oxepanes using Song's cation-binding oligoEG catalyst and KF as the base is demonstrated. A wide range of epsilon-, zeta-, and eta-hydroxy-alpha,beta-unsaturated ketones were cyclized to the corresponding five-, six-, and seven-membered chiral oxacycles with high enantiopurity. This remarkably successful catalysis can be ascribed to systematic cooperative cation-binding catalysis in a densely confined supramolecular chiral cage generated in situ from the chiral catalyst, substrate, and KF.