Asymmetric β-Elimination Of Secondary Sulfones Catalyzed By Chiral Cation-binding Polyether

First part: optimization of the polyethertethered chiral catalyst and building the catalyst libraryRecently, many chemists are focus on the polyethertethered chiral catalyst, what is one of the popular research area. But so far, the understanding of catalyst is still stay in the relatively shallow stage. This dissertation will surround the bottleneck of polyethertethered chiral catalyst to explore actively, such as: lack of systemic research, lack of Catalytic systems, limited scope of catalytic reaction and so on. It will be provide experimental and theoretical support to the design and development of polyethertethered chiral catalyst. Based on the existing catalyst, we have developed a series of novel polyethertethered chiral catalyst through different substituents at the 3,3’-positions of the BINOL unit to enrich the existing chiral catalyst library. Second part: Asymmetric β-Elimination of Secondary SulfonesThe asymmetric synthesis of secondary sulfones by a highly enantioselective β-elimination(kinetic resolution of secondary sulfones) catalyzed by chiral cation-binding polyether is reported. This transformation employs BINOL based polyether as the cation-binding catalyst and readily available potassium fluoride as the base, which is compatible with different substituted racemic sulfones and could provide an access to the preparation of enantiopure secondary sulfones in excellent enantioselectivity(ee value up to 99%, S factor up to 327). Preliminary mechanistic studies suggest that the reaction proceeds via a carbanion mechanism, involving initial β-proton-elimination by fluoride ion to afford β-carbanion intermediate and the consequent loss of Ph SO2- from α-carbon atom yields the olefinic product and unreacted enantiopure sulfones.