Design And Catalysis Research Of Cinchona Alkaloid-based Catalysts

Cinchona alkaloids were valuable chiral synthon in asymmetric catalysis,not only due to their cheapness and availability,but also because they contained multiple chiral centres which could be readily modified.Herein,we have designed a series of chiral catalysts based on the cinchona alkaloids,and investigated their catalytic performance in asymmetric reaction.Based on the unique layered structure,large specific surface area,and abundant surface oxygenated functional groups of GO,we have supported the amino-modified cinchona alkaloid on the surface of GO sheets through a thiol-ene click reaction.The resulted GO-supported cinchona alkaloid was characterized by XRD,FT-IR and chemical titration.The catalysts were employed in asymmetry direct aldol reaction of cyclohexanone and aromatic aldehydes in water,producing the corresponding chiral ?-hydroxy ketone in moderate,diastereoselectivities and enantioselectivity.Based on the phase-transfer ability of polyethylene glycol(PEG)and the positive effect of imidazolium-based ionic liquid(IL)on activating catalytically active species,we have designed a series of PEG-based di-imidazolium TL bridged cinchona alkaloid catalysts(PEG-IL-CN-n).Characterization technique confirmed the presence of PEG linker,imidazolium IL moiety and the cinchona alkaloid active site in PEG-IL-CN-n.Amphiphilic nature of PEG-based di-imidazolium IL moiety allowed the obtained catalysts to undergo inherent-phase transfer catalysis in asymmetry direct aldol reaction of cyclohexanone and aromatic aldehydes in water.As a result,chiral ?-hydroxy ketones were produced with moderate,diastereoselectivities and enantioselectivity.Based on the multiple chiral centre contained in cinchona alkaloid,we have designed a series of chiral cinchona alkaloid-based schiff Mn(?)complexes for enantioselective epoxidation of unfunctionalized olefins.The resulted chiral schiff Mn(III)complexes were characterized by FT-IR and UV-vis.Indeed,high yields of chiral epoxides were obtained over the cinchona alkaloid-based schiff Mn(III)complexes.