Thermal and magnetic dual-responsive l-proline nanohybrids for aqueous asymmetric aldol reaction

Thermal and magnetic dual-responsive l -proline nanohybrids ( l -Pro-based-TMNHs) were prepared by grafting thermal-responsive thiol-terminated P(NIPAM- co - l -ProlA)- b -POEGA-SH (PNLPO-SH) to vinyl-functionalized Fe 3 O 4 @SiO 2 -MPS through the thiol-ene click chemistry. The catalytic activity, selectivity and recyclability of l -Pro-based-TMNHs were evaluated in a model asymmetric aldol reaction of cyclohexanone and 4-nitrobenzaldehyde in water. Thermal responsiveness of the l -Pro-based-TMNHs induced self-assembly to produce a hydrophobic microenvironment in aqueous medium for catalyzing asymmetric aldol reaction. The catalytic performance can be tuned by the molar ratio of PNLPO-SH to Fe 3 O 4 @SiO 2 -MPS, and l -Pro-based-TMNHs-2 with a ratio of 1:6 exhibited best catalytic activity and selectivity. At 50 °C and 5 mol% catalyst loading, 94% conv., 81/19 anti / syn and 95% ee were obtained. On the other hand, magnetic responsiveness of the l -Pro-based-TMNHs facilitates catalyst separation and reuse in the presence of an external magnetic field , and these results indicated no loss of both catalytic activity and selectivity associated with the course of recycling.