Synthesis Of Enantiopure C₃-symmetric Ligand Derived From BINOL And Its Preliminary Application In Asymmetric Catalysis

The design of a new catalyst for asymmetric reactions is one of the key challenges and a highly important task in organic chemistry. In the design of a new catalyst framework, molecular symmetry plays one of the powerful guidelines. It often simplifies the transition states and reduces the number of the diastereomeric reaction sites to produce a favorable effect for enantioselectivity. Therefore,C₂-symmetric molecules have been widely found in both chiral ligand for metal catalyzed reactions and asymmetric organocatalysts. Compared to C₂-symmetric molecules, the studies on utilization of threefold symmetric molecules?C₃-symmetric molecules? are less commonly appeared. Receltly, chemists from all over the world has paid much attention to C₃-symmetry, especially in asymmetric catalysis and chiral molecular recognition. In particular, much progress has been made with C₃-symmetric catalysts for asymmetric transformations.Optically active with pendant of binaphthyl ligands have been widely used in various kinds of asymmetric catalytic reactions. Therefore, we set up a study aimed at incorporating such ligands into C₃-symmetric structures. Herein, we report the synthesis of novel C₃-symmetric dendritic molecular ligand containing three axially chiral binaphthyl subunits. This dissertation research content mainly consists of the following three parts:In the first part, we synthesized a novel C₃-symmetric dendritic ligand?S,S,S?-1,1,1-tri?4-?2,2?-dihydroxy-1,1?-binaphthyl-3-methoxy?phenyl?ethane?L1? with a high yield by six steps, which derived from commercially available?S?-BINOL.In the second part, the C₃-symmetric ligand?L1? was used to conduct the enantioselective addition of diethylzinc to aromatic aldehydes. The ligand could be easily recovered and reused almost without loss of catalytic activity as well as enantioselectivity. The optically active secondary alcohols were obtained with up to91% ee and up to 99% yields under relatively mild conditions. In addition, this novel C₃-symmetric ligand has shown higher enantioselectivities than its monomeric analogue?C1-symmetric ligand? in this reaction.In the third part, a chiral self-supported catalyst?L1/Zn? was prepared by used the C₃-symmetric ligand?L1? and diethylzinc. The catalyst was successfully applied in the enantioselective epoxidation of a range of?E?-?,?-unsaturated aromatic ketones.The products have good enantioselectivity with up to 76% enantiomeric excess?ee?.The self-supported catalyst?L1/Zn? was recovered from the reaction mixture only by washing process and was reusable for several consecutive runs.