Conformationally Rigid Chiral Bicyclic Skeleton‐Tethered Bipyridine <i>N,N′‐</i>Dioxide as Organocatalyst: Asymmetric Ring Opening of <i>meso</i>‐Epoxides

Abstract

Abstract 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 (SiCl 4 ). 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 °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. magnified image