Synthesis Of Chitosan Supported L-proline And Its Catalytic Capacities For Direct Asymmetric Aldol And Henry Reaction

Recently, the organic small molecule catalyst received more and more attention. Various organic small molecules as proline, binol, thiourea and biological bases were applied to catalyze various asymmetric reaction such as direct asymmetric aldol reaction, Henry reaction and Diels-Alder reaction and great achievements were obtained. Compared with the traditional chiral catalysts of enzyme and transition metal-chiral legend, the organocatalyst showed lots of advantages such as inexpensive, low toxicity and simply operation and gained more and more attention. However, the organocatalyst also owns some shortcomings as large dosage and difficult to recycle et.al. To overcome the shortcomings, in our work, chitosan was used as a legend to support well researched L-proline that one of the organocatalyst, by which a novel heterogenous catalyst was synthesized. Subsequently, the novel catalyst was applied to catalysze the direct asymmetric aldol reaction and asymmetric Henry reaction. The work was complished as bellow:1. The synthesis of chitosan supported L-prolineThe graft reaction was carried out via the reaction of activated carbonate acid and the amino group in L-proline. The intermediate and target product was characterized by IR, NMR, MS et al and it was conformed that the obtained product was the target complex.2. The catalytic properties of the chitosan supported L-proline for the direct asymmetric aldol reactionIt was showed that the direct asymmetric aldol reaction of p-nitrobenzaldehyde and acetone could be catalyzed by the novel catalyst in various media with good yields and enantioselectivities. Compared with the organic solvents, the catalyst showed better performance. With the decreasing of temperature, the enanoselectivity increased.In the asymmetric aldol reaction that contained two asymmetric points, moderate catalytic activity and stereoselectivity were showed. In the further research, compared with pure water, the aqueous micelle as the medium for the reaction was more suitable. As a heterogenous catalyst, the novel catalyst showed a good reusability.3. The catalytic properties of the chitosan supported L-proline for the Henry reactionTo widen the application, the catalyst was used to catalyze the Henry reaction of aromatic aldehyde and nitromethane that did not be well researched and in which the seteroselectivity was much more to be controlled. It was found that the catalyst could catalyze the reaction in various media and showed moderate catalytic activity, especially, in water and aqueous micelle, better results were obtained than in the organic solvents. However, different from the asymmetric aldol reaction catalyzed by the chitosan supported L-proline, the catalyst showed a lower steroselectivity in asymmetric Henry reaction.Interestingly, the chitosan was accidentally found to be an efficient catalyst for the Henry reaction. In the further research, the Henry reactions of various substances could be catalyzed by chitosan in various media. The catalyst showed a good reusability in the Henry reactions carried out in water.