Synthesis, Characterization And Catalytic Applications Of Magnetic Nanoparticles Immobilized Cinchona Alkaloid

Organocatalysis,bearing advantages of low toxicity,environmentally friendliness,mild reaction conditions,has attracted wide attention and interests from chemists.Organic chiral amines exhibited excellent catalytic performances in many asymmetric reactions,especially for natural products represented by cinchona alkaloids in recent years.Meanwhile,easy separation and recycling of catalyst is a hot topic with great concern from researchers.Immobilization is a simple,economic,high-efficient method which showed outstanding catalytic ability and reusing performances in recent reports.Hence,we summarized the advances in asymmetric reactions promoted by chiral amine organocatalysts(especially cinchona alkaloid)and immobilized cinchona alkaloids.Then,we put forward the following research project.In this situation,we synthetized several kinds of immobilized cinchona alkaloid catalysts.Solid support was prepared by co-precipitation and sol-gel method,which was followed by coupling with functional cinchona alkaloid.Synthesized catalysts were characterized by IR,NMR,XPS,SEM,EA etc.Then,asymmetric Michael addition reaction between 1,3-dicarbonyl compounds and N-substituted maleimide was chosen as a model reaction using this catalyst.Solvent effect,temperature effect and concentration effect were investigated in this reaction.We found 1 mmol of substrate,2 mL of toluene and 20 mol%catalyst usage in 0~oC was the best reaction condition.Reaction substrates were also broadened in this reaction which was completed in good-high yield(53-91%)and high stereoselectivity(93%ee,88:12 dr).Recycling ability was also tested in this reaction and no obvious loss in catalytic activity was observed after three runs.In addition,this type of catalyst was employed in catalyzing asymmetric aldol reaction,nitro-Michael addition reaction and MBH reaction as well.Aldol reaction between trans-?-nitrostyrene and dimethyl malonate was finished in high conversion and enantioselectivity.However,the reusing ability of catalyst was poor in this reaction.Meanwhile,it exhibited good-high catalytic performance in nitro-Michael addition reaction of cyclohexanone and p-nitrobenzaldehye.In asymmetric MBH reaction,although high enantioselectivity was achieved,the yield was comparatively low.