Studies On The Synthesis And Asymmetric Catalytic Behaviors Of Novel Chiral Bifunctional Organocatalysts

In recent years, organocatalysis has been proven to be one of the most rapidly developing and competitive research areas in asymmetric catalysis, and has become a third branch besides biocatalysis and transition metal catalysis. Thiourea-based and squaramide-based organocatalysts evolved as an efficient class due to its unique characteristic of a dual hydrogen-bonding donor. A number of research groups have proven that catalysts with bifunctional moieties could promote asymmetric transformations more efficiently.In this thesis, the isostiviol which is an inexpensive and readily available natural product possessing a hydrophobic skeleton was transformed. Twelve novel amine-thiourea type or amine-squaramide type organocatalysts were designed and synthesizedIn the following study, firstly, enantioselective Michael addition of 4-hydroxycoumarin and β,γ-unsaturated α-ketoesters catalyzed by the synthesized catalysts was investigated. High isolated yields(up to 97%) and enantioselectivities(up to 96% ee) were obtained with Cat-2a as the catalyst under the optimized conditions. The transition state to account for the stereochemical outcome of this catalytic system was proposed.Secondly, in the asymmetric Michael addition of aldehyde to N-substituted maleimides, two chiral primary amine-squaramide organocatalysts Cat-6a and Cat-6b with different configurations both exhibited excellent catalytic performance, opposite configuration of products were obtained in good yields(up to 98%) and excellent enantioselectivities(up to >99% ee). Also, the possible working model of transition state was proposed.