The Application Of The Two-Phase System In The Organocatalytic Asymmetric Cascade Reactions

There are many advantages of asymmetric organocatalysis,such as environmentally-friendly,simple and efficient,high selectivity,mild reaction condition,cheap and readily available catalysts,which meet the requirements of the modern green chemistry.In this dissertation,the application of the two-phase system in the organocatalytic asymmetric cascade reactions which would generate proton acid during the reaction was mainly discussed.In the organic/water two-phase system an inorganic base was introduced to neutralize the generated proton acid during the reaction,and was expected to transfer the proton acid to water phase,so as to improve the efficiency of the reaction.Based on this strategy,two types of organocatalytic asymmetric cascade reactions in two-phase system were further studied by using chiral amine-squaramide bifunctional catalysts.Initially,dimedone and bromonitrodialkene was used as the model reaction to explore the feasibility of the two-phase system in the Michael/S_N2 cascade reaction.Based on the optimized reaction conditions,with 1,2-dichloroethane-water as the solvent,reaction results demonstrated that the reaction could afford excellent enantioselectivity(>99%ee)in the presence of bifunctional chiral catalyst(5 mol%).At the same time,the absolute configuration of the product has been confirmed through the X-ray diffraction.In addition,the two-phase system was also introduced to the Friedel-Crafts/Substitution cascade reaction of phenolic compounds.?-Naphthol and bromonitrodialkene were used as the model reaction.The reaction conditions were optimized and the substrates bearing various substitutions were also examined.Reaction results showed that with chloroform-water as the solvent,the reaction could achieve high isolated yield(up to 99%)and excellent enantioselectivity(up to>96%ee).The absolute configuration of the product has also been confirmed through the X-ray diffraction.Our study results showed that the two-phase system is of great reference value,which can perform as an easy to operate and environmentally-friendly method in the organocatalytic asymmetric cascade reactions which would generate proton acid during the reaction.We will continue to explore the application of the two-phase system in other similar series of reactions.