Recyclable L-Proline Catalysis Systems Catalyze Direct Alold Reaction In Water

Chiral compounds are ubiquity, but in the field of pharmaceutical synthesis. Most of the two enantiomers of chiral compounds have different or even opposite biological activity and function. A single configuration of enantiomers was needed. Asymmetric synthesis solved this problem. L-proline is small organic molecules catalyst for the C-C bond forming. It attracts more attention in the field of asymmetric catalytic synthesis due to its stability in the water and air, easy preparation and application, non-toxic harmless properties. In the view of economic and environmental protection, it is desired that organic reactions can carry out in green solvent and the catalysts can be repeated and recycled. In this paper, L-proline was derived and ?-cyclodextrin functionalized magnetic nanoparticles were introduced to design two recyclable catalytic systems which can catalyze direct asymmetric Alold reaction in water.First, a novel N-4-tert-butylbenzenesulfonyl-L-proline amide organocatalyst was successfully prepared and its catalytic performance was evaluated in the direct aldol addition of cyclohexanone and p-nitrobenzaldehyde. Significantly improved reactivity and stereoselectivity were achieved in various solvents especially in water. Furthermore, substituent effect on direct aldol addition of cyclohexanone and benzaldehyde derivates has been studied. Evidence was found that, although the catalyst has a hydrophobic group, it possessed strong polar and worse solubility in organic solvent. Thus, recycling and re-usage of catalyst was possible by extraction of the product with ethyl acetate and the remainder water with catalyst was used for next run without further purification.In addition, ?-Cyclodextrin modified magnetic nanoparticles Fe3O4@SiO2-?-CD were added to provide a hydrophobic pocket which can provide homogeneous reaction centers for water reaction to decrease the usage amount of ketone. Meanwhile recycling and re-uasege of catalyst was possible by magnetic separation without the use of extraction organic solvent and loss of catalyst. Tthe catalyst system can be used for another five runs without lower activity.