Preparation Of Nature Polymer Supported Cinchonine Catalysts And Their Catalytic Properties For Asymmetric Reactions

Small organic molecule catalysis is one of the recent hotspots in the field of asymmetric synthesis.Along with continuous deepening of the research on L-proline, cinchona alkaloids and other small organicmolecules, various shortcomings such as large dosage and recovery difficulty of small organic moleculecatalysts gradually emerge. To offset these deficiencies, polymer-supported catalysts emerge in response todemand. Many currently available polymer-supported catalysts use synthetic polymers such as polystyreneand polyethylene glycol as the carrier. In the present research, with a perspective to green chemistry andsustainable development, we choose natural macromolecules including carboxymethyl cellulose,carboxymethyl starch and chitosan as the carrier to synthesize four kinds of polymer chiralcatalysts——natural macromolecules loaded cinchona alkaloid (cinchonine). As-obtained polymer chiralcatalysts were used to catalyze asymmetric Michael reaction, direct asymmetric Aldol reaction, andMannich reaction; and their structure and catalytic performance were examined. The main content andresults of this thesis are as follows:1. Two kinds of polymer-supported cinchonine catalysts were synthesized by the reactions ofcarboxyl-containing natural macromolecuels carboxymethyl starch or carboxymethyl cellulose withcinchona alkaloid (cinchonine). Resultant catalysts were used to catalyze the asymmetric Michael reactionof1,3-dicarbonyl compounds and N-benzyl maleimide. The effects of solvent, catalyst dosage, andsubstrates on the catalytic performance were systematically investigated, and the reusability of the catalystswas also evaluated. Findings indicate that the two kinds of as-synthesized catalysts can effectively catalyzethe aforementioned reactions, and carboxymethyl starch-supported cinchonine exhibits better activity andstereoselectivity. Besides, the two catalysts can be readily separated from the reaction systems and exhibitgood reusability.2. Cinchonine-succinic anhydride was grafted onto natural macromolecule chitosan containing abundant ofamino group and hydroxyl group to afford chitosan-supported cinchonine catalyst. The intermediates andtarget product were characterized and confirmed by nuclear magnetic resonance spectrometry, massspectrometry, and infrared spectrometry. Moreover, the catalytic performance of as-synthesized chitosan-supported cinchonine catalyst for the asymmetric Aldol reaction between aromatic aldehydes andcyclic ketones was determined. Results indicate that, in the presence of0.2mL water as the solvent,as-synthesized chitosan-supported cinchonine catalyst exhibits the best catalytic performance (ee value96%, dr value24:76, yield>99%), and it can be recycled at least five times without significant loss ofcatalytic activity.3. Thiourea was introduced into loaded chiral catalyst through the reaction between cinchonin-isothiocyanate and chitosan to afford chitosan supported thiourea-cinchonine bifunctional catalyst. Thechemical structure of the target product was confirmed by infrared spectrometry. Furthermore,as-synthesized bifunctional catalyst was used to catalyze the direct asymmetric Aldol reaction betweencyclohexanone and aromatic aldehydes containing different substituents, and its catalytic performance wasdetermined. Results indicate that, in the presence of water as the reaction medium, as-synthesized chitosansupported thiourea-cinchonine bifunctional catalyst exhibits good catalytic performance (yield99%) andstrong stereoselctivity (ee value91%). Besides, the catalyst can be recovered and reused for5timeswithout change in activity.Moreover, the catalytic performance of the four kinds of as-synthesized polymer-supported chiral catalystsfor the three-component asymmetric Mannich reaction of aromatic aldehydes, aniline and hydroxyacetonewas also evaluated for extending their application scopes. Findings indicate that, in the presence ofN,N-dimethyl formamide as the solvent, chitosan-supported thiourea-cinchonine catalyst shows goodrecyclability for the aforementioned three-component asymmetric Mannich reaction, but its selectivity isunsatisfactory.