Asymmetric reactions of unsaturated esters and desymmetrizations of P-stereogenic phosphinates via carbene catalysis and oxidative carbene catalysis
Date of Issue2016
School of Physical and Mathematical Sciences
This thesis focuses on esters activation and desymmetrization for enantioselective reactions enabled by N-heterocyclic carbenes (NHCs) organocatalysts. It contains four parts: Chapter 1 gives brief introductions to the history and development of NHC catalysis classified by common active intermediates within this field. Representative examples and furture challenges are summarized and reviewed as well in this part. Chapter 2 describes a formal LUMO activation of α, β-unsaturated esters enabled by NHC catalyst for highly enantioselective lactam formation. Sterically bulky β, β-disubstituted esters can also be used in this strategy, which delivers the optically enriched product containing a quarternary carbon center. Chapter 3 is about NHC-catalyzed cascade reaction for synthesis of functionalized pyrrolo[3,2-c]quinolones. The products from Michael-Mannich-Lactamization cascade reaction are obtained in good yield and enantioselectivity with three consecutive stereogenic centers. Chapter 4 introduces a rapid approach to P-stereogenic phosphinates via NHC-catalyzed desymmetrization of bisphenols. Due to the high efficiency of the reaction, the enantiomerically enriched P-stereogenic phosphinates can be prepared in large scale under low catalyst loading. The chiral phosphinates are also demonstrated as a good catalyst in the reductive aldol reaction.