Preparation Of Polyamino Acids Catalysts By End-modification With Quanternary Ammonium Salt And Their Application In Asymmetric Epoxidation Of α,β-Unsaturate Ketones

In this thesis, the novel polyamino acids modified by quaternary ammonium salt were synthesized and used as the catalyst for asymmetric epoxidation ofα,β-unsaturated ketones.1. A series of quaternary ammonium salts possessing a free terminal amino group were designed and prepared which includes 3-(3-aminopropyl)-1-methyli midazolium chloride,3-(2-(2-aminoethoxy)ethyl)-1-methylimidazolium chloride,3-(2-(2-(2-aminoethoxy)ethoxy)ethyl)-1-methylimidazolium chloride,1-((1-(2-(2-ami noethoxy)ethyl)-1,2,3-triazol-4-yl)methyl)-2,6-dimethylpyridinium chloride. All the structures of the products were characterized by IR and NMR spectra.Using the up-mentioned functionalized quaternary ammonium salt as an initiator initiated the polymerization of N-carboxyanhydride of L-amino acid, five novel polyamino acids, Poly-L-alanine (PLA), Poly-L-valine (PLV), Poly-L-leucine (PLL-2, PLL-3, PLL-4) were obtained, and the structures of the polyamino acids were characterized by IR spectra and elemental analysis..2. Application of the polyamino acid catalysts in the asymmetric epoxidation ofα,β-unsaturated ketones(1) The catalytic activities of the modified polyamino acid catalysts were tested with epoxidation of chalcone as the model reaction. The results indicated that the poly-L-leucine and poly-L-valine showed better catalytic effects than poly-L-alanine. Meanwhile, the recycle experiments showed that poly-L-leucine exhibited better enanatioselectivity and catalytic stability than poly-L-valine.(2) The modification of the catalyst with an alkoxy-bridge in the part of end-quaternary ammonium salt could accelerate the epoxidation reaction. Without pre-activation, the PLL-2 made the reaction nearly complete after only 2h. In the recyle experiment, only 30 min reation time was needed..(3) The introduction of the ionic terminal group ameliated the appearance and property of the polyamino acid, and the powered-like catalyst could be easily separated and reused, and the loss was lower than 2%.(4) The extension of alkoxy-bridge chain of the catalyst could further accelerate the rate of the epoxidation reaction, but it is not favourable to the stability of the catalyst.(5) The catalyst which possessing a single alkoxy-bridge chain is of excellent stability, and after eight recycles, the catalytic activity and the product's enantioselectivity were retained completely.(6) The amount of traditional catalysts required is generally 20 mol% relative to the substrate. When the molar ratio of the catalyst PLL-2 was decreased to 5 mol%, the yield of 89% and 90% enantioselectivity were still obtained.(7) The epoxidation of various (E)-α,β-unsaturated ketones was examined using the modified catalyst, PLL-2, and almost all of the substrate gave the the corresponding epoxides in good yields and enantioselectivities after only 30 min. The ee% value was upwards 95%-97% with the yield>90%.