Synthesis Of Chiral Ionic Liquid And Application Of Chiral/Achiral Ionic Liquids In Catalytic Benzoin Reaction

Considerable attention has really been focused on ionic liquids (ILs) as "green" alternatives to classical environmentally damaging organic solvents in many fields such as in organosynthesis, material, catalysis, electrochemistry, biochemistry, physicochemistry, separation and so on. However, there have been only a few examples of chiral ILs have been reported so far, and ILs possessing chirality are having been synthesized aimed at application in asymmetric catalytic reaction. In fact, the application of chiral ILs in asymmetric catalytic transformations is still at a preliminary stage.Benzoin is an important intermediate in organosynthesis. And more than, chiral benzoin is important structure unit of many bioactive compounds and building blocks (chiron) of many enantioselective synthesis.Benzoin condensation reaction is usually promoted by toxic cyanide ion, so the development of more convenient and efficient synthetic methods, which is environmental benign, is highly desired. In this thesis, the emphasis is on the research of synthesis of a novel chiral imidazolium salt and application of chiral/achiral imidazolium salt in catalytic benzoin condensations.Benzoin condensation reaction of benzaldehyde using simple imidazolium based ionic liquids as catalyst has been successfully achieved. The reaction factors such as solvent, base and ionic liquids have been studied in detail. The result showed simple imidazolium based ionic liquids had excellent catalytic activity, especially when under mild conditions with 0.5 equiv. EMIMBr / K₂CO₃(1 /1.1) in CH₂Cl₂, the desired benzoin was obtained in yield of 86%. ILs can be reused five times without significant loss of activity, yield of 76% still. Under optimized conditions, the reactivity of a series of similar substrates to substituted benzoins was also examined and moderate to good yield were obtained. Based on the results of this reaction, the possible mechanism of the benzoin condensation reaction was shown briefly.We have designed and prepared a new family of chiral imidazolium based ionic liquids(identified by NMR and IR et al.) based on amino acids derived from the chiral pool by a simple and straightforward procedure, and the induction ability of chiral imidazolium salt for asymmetric catalytic benzoin condensation reaction has been probed. Nevertheless, low enantioselectivity has been detected, and more work would be performed for enantioselective processes in the future.