The Preparation Of Hairy Polymer Microspheres Immobilized With Chiral Catalysts And Application In Asymmetric Aldol Reaction

The polymer brush that on the surface of hairy particles is a fluid dynamics system, which unlikeimmobilized small molecules via covalently totally fixed on the surface of solid particles, so hairy particlessupported catalysts can combine the advantages of both homogeneous catalysts (highly active, highselectivity) and heterogeneous catalysts (easy separation, recovery reuse). Firstly, using the method ofRAFT precipitation copolymerization, we obtained functional polymer microspheres with chain transfergroup; then we prepared chiral catalyst loading (L-proline and Macmillan amine) of hairy polymermicrospheres. By RAFT surface graft polymerization. Furthermore, the achieved hairy particles was usedin asymmetric synthesis reactions as catalysts. The article has mainly researched the influence of hairynanoparticle structure on catalytic activity, asymmetric selectivity and recyclability. The article has revealedthe nature of asymmetric reactions catalyzed by hairy nanoparticles grafted with chiral polymer brushes,and has provided theoretical basis for design and development of new high efficiency and high selectivehairy nanoparticles supported chiral catalyst.(1)Synthesis and characterization of hairy polymer microspheres immibilized with Poly(O-methylacroloyl-L-hyp)： L-hyp and methyl carbonyl chloride reacted in the trifluoro acetic acid to prepareO-methyl acroloyl-L-hyp hydrochloride. Then polymerizable monomer N-substituted Boc–O-methylacroloyl-L–hyp was obtained from the Boc anhydride protection of O-methyl acroloyl-L-hyp hydrochlorid.The polymer micropheres with surface-immobilized dithioester groups were prepared via RAFTprecipitation polymerization (RAFTPP), and hairy polymer microspheres grafted with polymeric chainswith N-Boc-hyp were obtained from surface of micropheres by reversible addition fragmentation activeradical polymerization (RAFT) technical. Finally hairy polymer microspheres grafted with Poly(O-methylacroloyl-L-hyp) were achieved by deprotection of catalyst. The formation of the catalysts wascharacterized by nuclear magnetic resonance (NMR), IR spectra, scanning electron microscope (SEM) andelemental analysis.(2)Synthesis and characterization of hairy polymer microspheres immobilized with Poly[(S)-5-(4-methacryloyloxy benzyl)-2,2,3-trimethyl-4-Imidazolidin]: First of all, we prepared MacMillan chiral amine, being called (S)-5-(4-acrinyl)-2,2,3-trimethyl-4-Imidazolidin with L-tyrosine, then (S)-5-(4-methacryloyloxy benzyl)-2,2,3-trimethyl-4-Imidazolidin hydrochloride was prepared by MacMillan chiralamine reacted with methyl carbonyl chloride in the trifluoro acetic acid, finally polymerizable monomer(S)-5-(4-methacryloyloxy benzyl)-2,2,3-trimethyl-4-Imidazolidin was prepared in the reaction of (S)-5-(4-methacryloyloxy benzyl)-2,2,3-trimethyl-4-Imidazolidin hydrochloride with triethylamine followed bytreatments of neutralizing with triethylamine. The polymer micropheres with surface-immobilizeddithioester groups were prepared via RAFT precipitation polymerization (RAFTPP), and hairy polymermicropheres grafted with polymeric chains containing MacMillan chiral amine were obtained from surfaceof micropheres by surface-initiated reversible addition fragmentation active radical polymerization (RAFT)technical. The catalysts were characterized by nuclear magnetic resonance (NMR), IR spectra, scanningelectron microscope (SEM) and elemental analysis.(3)The application of hairy polymer microspheres supported with chiral catalysts in asymmetricsynthesis reations:Hairy polymer microspheres grafted with Poly(O-methyl acroloyl-L-hyp) were carried out inasymmetric direct aldol reaction, the influence of reaction condition on performance of as-prepared catalystwas investigated and the optimum reaction conditions were therefore determined. The performance andreusability of as-prepared catalyst under the optimal condition were studied. The experiment results showthat hairy polymer microspheres in the typical aldol reaction of4-nitrobenzaldehyde and cyclohexanone,have good catalytic activity and enantioselectivity. The experiment results show that this catalyst inasymmetric aldol reaction of4-nitrobenzaldehyde with cyclohexanone performs better catalytic activity andenantioselectivity (99%yield and96%ee value) in optimized reaction conditions(DMF/water95/5assolvent,20mol%catalytic amount and in0℃). By simple separation, catalyst can be recovered and reused.