A solution to achieve good reusability of MNPs Fe3O4-supported (S)-diphenylprolinoltrimethylsilyl ether catalysts in asymmetric Michael reactions†
Abstract
A new supported (S)-diphenylprolinol trimethylsilyl ether (Fe3O4/PVP@SiO2/ProTMS) using polyvinylpyrrolidone (PVP)-modified MNPs Fe3O4 as a support was prepared via one-pot surface-modification, and exhibited high yield (93–99%), excellent diastereoselectivities (syn/anti = 81–96 : 19–4) and enantioselectivities (95–98% ee) in the asymmetric Michael addition of propanal to various nitroalkenes. TGA, XRD, IR, SEM, TEM, elemental analysis and N2 adsorption–desorption isotherm demonstrated that the adsorption of PVP onto MNPs Fe3O4 resulted in the spectacular change in the chemical composition, surface morphology and pore structure of Fe3O4/PVP@SiO2/ProTMS. The catalyst could be easily separated from the reaction by an external magnet and reused for ten times with high yields (77–99%) and unchanged excellent stereoselectivities (97–98% ee and syn/anti = 96/4) in the Michael addition for the first time.