Conformationally Rigid Chiral Bicyclic Skeleton-Tethered Bipyridine N,N′-Dioxide as Organocatalyst: Asymmetric Ring Opening of meso-Epoxides

The conformationally rigid chiral bicyclic skeleton tethered bipyridine N,N'-dioxide (-)-9 has been designed, synthesized and examined as an organocatalyst in the enantioselective ring opening of meso-epoxides using tetrachlorosilane (SiCl4). The catalyst (-)-9 is found to exhibit good enantioselectivity for substituted cis-stilbene epoxides; whereas, the saturated cyclic meso-epoxides display a moderate enantioselectivity. At -30 degrees C in chloroform, the catalyst (-)-9 with 0.5 mol% loading generated the chlorohydrins in up to 97% yield with up to 93% ee. The possible creation of transient axial chiral environment around hypervalent silicon species due to the presence of conformationally rigid chiral bicyclic skeleton tethered bipyridine N,N'-dioxide may be responsible for such enantioselectivity observed in the desymmetrization of meso-epoxides.