Preparation Of Poly-L-leucine Catalysts Modified By Quaternary Ammonium Salt And Application In Juliá-Colonna Reactions

This thesis aimed to develop effective and recyclable catalyst for high enantioselective asymmetric epoxidation ofα,β-unsaturated ketone based on our group's previous work,which includes two parts:1.Molecular design,preparation and characterization of novel poly-L-leucine catalyst modified by quaternary ammonium saltUsing functionalized quaternary ammonium salt,which carried a free amino group,as an initiator initiated the polymerization of N-carboxyanhydride of L-leucine (L-Leu NCA),it gave four new poly-L-leucine catalysts.The catalysts were characterized by IR spectra and elemental analysis.The introduction of the ionic terminal group ameliated the appearance and property of the poly-L-leucine,and the powered-like catalyst could be easily separated and reused.2.Application of the novel catalyst in Juli(?)-Colonna reaction(1)The catalytic activities of the quaternary ammonium salt modified poly-L-leucine catalysts were tested with epoxidation of chalcone as the model reaction.All the four catalysts,without pre-activation,showed satisfactory activity and enantioselectivity with the yield up to 89-91%,and the enantioselectivity 89-97% while the traditional catalyst n-BuNH₂-PLL only gave 66%of yield with 61%ee.(2)The recover and reusability of the new catalysts were investigated,and the results showed that the catalytic activity and enantioselectivity were almost retained after 7 times recycles.The average loss of the catalyst was amounted to 1-5%per run. When use 52 as the catalyst the yield was up to 98%with 97%ee in the recycle.(3)The temperature effect for the activity of the catalyst was also studied.It was found that the reaction rate was slowered when decease the reaction temperature from 25℃to 0℃,and the enantioselectivity improvement was not obvious.(4)The epoxidation of various(E)-α,β-unsaturated ketones was examined using the modified catalyst,and all of the olefins tested afforded the corresponding epoxides in good yields and enantioselectivities.Especially for the epoxidation of chalcones derived from substituted acetophenone,the ee%value was upwards 96%-98%,and there is no obvious electron and steric effects.(5)The amount of traditional catalysts required for Juli(?)-Colonna reaction is generally 20 mol%relative to the substrate.When the molar ratio of catalyst 52 was decreased to 5 mol%,the yield was almost retained,and the enantioselectivity was only 5%lower.For a further decrease to 1 mol%catalyst,90%enantioselectivity were still obtained.