Catalytic Asymmetric Intra- and Intermolecular Haloetherification of Enones: An Efficient Approach to (-)-Centrolobine

A catalytic asymmetric intra- and intermolecular haloetherification of electron-deficient alkenes (halogen = Cl, Br, I) has been realized by the use of chiral metal complexes of N,N'-dioxides. In the presence of a chiral Fe(III) complex, a series of tetrahydropyran derivatives were obtained in good yields (up to 99% yield) with a high level of enantioselectivities (up to 97% ee). Promoted by a chiral Ce(III) complex, chiral oxepane derivatives could be given in good results. Moreover, the intermolecular haloetherification of chalcones catalyzed by Sc(III) complex using MeOH as nucleophile is demonstrated. This methodology also can be successfully applied to the synthesis of (-)-Centrolobine. Meanwhile, a reasonable reaction mechanism was proposed.