Approaches to Asymmetric Catalysis Mediated by Ploymer-Supported and Homogeneous Organocatalysts

Identificador:  TDX:2784

Handle: https://hdl.handle.net/20.500.11797/TDX2784

Autors:  Wang, Shoulei

Resum:
This thesis focuses on the synthesis of organocatalysts, especially polymer-supported ones and their application in various asymmetric transformations. In Chapter II, an efficient, highly regio- and stereoselective [4+2] cycloaddition between alkylidene pyrazolones and enals through H-bond-directing dienamine catalysis has been developed. Chapter III describes a robust, highly efficient polystyrene-supported (PS) isothiourea organocatalyst in a variety of formal [4+2] cycloaddition reactions. In addition, recyclability of the immobilized isothiourea catalyst (11 cycles, accumulated TON of 76.8) and its application in continuous flow process (no decrease in yield or ee after 18 h) are also demonstrated. Chapter IV investigates an asymmetric periselective [8+2] higher-order cycloaddition between chiral ammonium enolates and azaheptafulvenes catalyzed by an immobilized isothiourea catalyst. The resulting [8+2] cycloadducts can also undergo completely regioselective [4+2] cycloaddition with active dienophiles to afford bridged polycyclic products in a straightforward manner. The last Chapter focuses on the cascade deoligomerization/cross-aldol reactions of electron-poor benzaldehydes or η6-benzaldehyde Cr(CO)3 complex with paraldehyde can be promoted by a dual catalytic system. Moreover, the obtained products can be easily transferred to medicinal drugs or natural product intermediates.