Application Of Imidazolium Ion-Tagged Organocatalyst In Asymmetric Catalysis Reaction

This thesis mainly focused on synthesis of two novel functionalized chiral ionic liquids and their application as organocatalysts for a-aminoxylation of aldehydes and ketones, a-amination of aldehydes and epoxidation of a, P-enones; Moreover, two kinds of organocatalyst can be recycled and reused. No decrease in their catalytic activity. Most important, the whole process was friendly to environment according to the conception of "green chemistry"In the first part, the recent progress of ionic liquids and chiral ionic liquids in organic synthesis was briefly reviewed.In the second part, Imidazolium Ion-Tagged Proline was synthesized from cheap and readily available starting material-proline. We investigated its application in asymmetric a-aminoxylation of aldehydes and ketones with nitrosobenzene in [bmim] BF4. At room temperature, high enantioselectivities and satisfactory yields were obtained at room temperature in the presence of 10 mol% chiral catalyst in twenty minutes. Furthermore, after a simple work-up, the catalyst / [bmim] [BF4] system could be easily recycled and retained similar reactivity as well as enantioselectivity after seven recycles.In the third part, the direct asymmetric a-Amination of aliphatic aldehydes with two kinds of dibenzyl azodicarboxylate was investigated using the chiral ionic liquids mentioned above. We optimized reactions conditions, such as catalyst loading temperature and solvents. Compared with the traditional oganic solvents, reaction speed, the chemical yields and enantioselectivities were all enhanced. Under the optimized protocol, employing 10 mol% catalyst in [bmim] BF4 at 0℃, The desired a-aminated alcohols were obtained with high chemical yields (89-96%) and excellent enantioselectivities (92-98% ee). By the same token, after simple process, the ionic liquid residue containing catalyst was dried under vacuum for about 60 min at 60℃, and reused for the next run of reaction. This procedure could be repeated for four times and the product could be obtained without significant decrease in enantioselectivities and yields.In the fourth parts, Imidazolium ion-tagged a, a-bis (3,5-dimethylphenyl)-(S)-pyrrolidin-2-ylmethanol was synthesized from trans-4-hydroxy-L-proline. TBHP as the oxidant, a series of different trans-a,p-unsaturated ketones were evaluated under the optimized reaction conditions employing 20 mol% catalyst in hexane at 0℃. High yield (up to 94%) and excellent enantioselectivity(up to 96% ee) have been obtained. Effects of Substituted groups with of different electronic and steric characters on the results were also discussed. The chiral ionic liquid can also be recycled and resued at least for five runs without obvious decrease in its catalitic activity.