Synthesis And Asymmetric Catalytic Performance Of Graphene Oxide Supported Proline Derivatives

As a green and inexpensive small molecule chiral catalyst,proline has good application prospects.However,the small molecule catalyst is difficult to reuse,so the proline derivative is loaded on the carrier to obtain the supported catalyst,which can be recovered and reused.Graphene oxide（GO）has good hydrophilicity and a layered structure,which is conducive to the progress of the catalytic reaction and is a good choice of carrier.In this thesis,three proline derivatives were synthesized,three proline derivatives were loaded on GO to obtain three supported catalysts,and the supported catalysts were used to catalyze the asymmetric Aldol reaction and Michael addition reaction to study its asymmetric catalytic performance.Proline methyl ester（Pro-OCH₃）was synthesized by substitution reaction,and two proline dipeptide derivatives with Fmoc protecting group Fmoc-d Pro-OCH₃ and Fmoc-Hyp-Pro-OCH₃ were synthesized by amidation reaction of Pro-OCH₃ with Fmoc-L-proline and Fmoc-L-hydroxyproline.The Fmoc protecting group was removed with morpholine to obtain two proline dipeptide derivatives d Pro-OCH₃ and Hyp-Pro-OCH₃.The structure of the synthesized substances was characterized by FT-IR and ¹H NMR,which proved that the target products have been successfully synthesized.Dissolved Pro-OCH₃,d Pro-OCH₃ and Hyp-Pro-OCH₃ in water,and used ultrasound to load them on the GO through the hydrogen bond and ion interaction between the amino group of the proline derivative and the oxygen-containing functional group of GO.Then,three supported catalysts of graphene oxide supported proline derivatives Pro-OCH₃/GO,d Pro-OCH₃/GO and Hyp-Pro-OCH₃/GO were obtained.FT-IR characterization and TGA analysis proved that the derivatives were successfully loaded on GO.The supported catalyst had a layered structure observed by SEM,which was beneficial to the progress of the catalytic reaction.Three supported catalysts and their corresponding small molecule derivatives were used to catalyze the asymmetric Aldol reaction and（reaction substrates are acetone and4-nitrobenzaldehyde）and Michael addition reactions（reaction substrates are cyclohexanone and trans-β-nitrostyrene）.Pro-OCH₃ has one chiral catalytic site,d Pro-OCH₃ and Hyp-Pro-OCH₃ have two chiral catalytic sites.The increase of chiral catalytic site made d Pro-OCH₃/GO and Hyp-Pro-OCH₃/GO have better catalytic effects than Pro-OCH₃/GO in the two catalytic reactions.When d Pro-OCH₃/GO catalyzed Aldol reaction,the effect was better than Hyp-Pro-OCH₃/GO,and when catalyzed Michael addition reaction,Hyp-Pro-OCH₃/GO had better catalytic effect.Compared with the corresponding small molecule catalytic effect,the supported catalyst did not decrease,because its layered structure facilitated the catalytic reaction and maintained a good catalytic effect.The catalytic effect of the supported catalysts in different solvents were also different,and the supported catalysts had good dispersibility in water and had achieved good catalytic effects in water,which was in line with the concept of green chemistry.The lower reaction temperature facilitated the two catalytic reactions.The supported catalysts were easy to separate from the reaction system and can be reused.After reused for 3 times,the ee value,syn/anti value and yield of the catalytic product are maintained at a high level.