Core–shell silica magnetic microspheres supported proline as a recyclable organocatalyst for the asymmetric aldol reaction

l-4-Hydroxyproline has been successfully grafted onto the core–shell structural silica magnetic microspheres and characterized by elemental analysis, thermo gravimetric analysis (TGA), vibrating sample magnetometry (VSM), high resolution transmission electron microscopy (HRTEM) and Fourier transform infrared (FT-IR). The chiral immobilized catalyst demonstrated high catalytic activity (up to 92%), diastereoselectivity (up to 85:15) and enantioselectivity (up to 80%) in the asymmetric aldol reaction between aldehyde acceptors and ketone donors. On the other hand, the synthesized catalyst could be rapidly separated from the reaction mixture through an external magnetic field and reused up to five runs without any obvious loss of activity, indicating its easy-separated property and excellent recyclability.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (537 K)Download as PowerPoint slideHighlights► This immobilized catalyst has regular spherical core–shell structure. ► Our catalyst has high activity and stereoselectivity in the direct aldol reaction. ► This catalyst has good dispersion, magnetic separation ability and recyclability. ► The Fe3O4@SiO2 nanoparticles also have some activity in the aldol reaction.