Asymmetric Cycloetherification by Bifunctional Organocatalyst

Attempts to obtain enantiomerically enriched tetrahydrofuran derivatives via an intramolecular oxy -Michael addition reaction of epsilon-hydroxyenone is discussed. Despite previous difficulties associated with the asymmetric induction of this reaction, which can proceed even without a catalyst, a highly efficient asymmetric induction was realized using a bifunctional organocatalyst derived from a cinchona alkaloid. The reaction could be extended to -hydroxyenone to yield an optically active tetrahydropyran derivative with a high ee. In these reactions, it is important for the gentle acidic and basic sites in the bifunctional organocatalyst to be arranged properly within the molecular skeleton of the catalyst. The high performance asymmetric induction relied on the affinity of the catalyst for the substrate, which played an important role. A disubstituted tetrahydropyran synthesis could be effectively performed via kinetic resolution using -hydroxyenone containing a secondary alcohol moiety using a chiral phosphoric acid catalyst.