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.