Organic Reactions In Microreactor Of Cyclodextrins

It's a new topic for chemists to research on modeling the function of cell's environment and enzymes via microreactors.As an important microreactor,cyclodextrin(CD) is attracting more and more attention. Cyclodextrins are a class of cyclic oligosaccharide molecules normally comprised of six(α),seven(β) or eight(γ)α-1,4 linked D(+)-glucopyranose unite,in which the interior surface of the cavity is hydrophobic and the external surface is hydrophilic.They are well known for their ability to form inclusion complexes with a wide variety of guest molecules ranging from organic molecules to inorganic compounds and ions in aqueous solution.Cyclodextrins can be used as chiral microreactors because of their ability of asymmetric induced chemical reactions.Cyclodextrins are also efficient inverse phase transfer catalysts(IPTC) for they are soluble in water and can form inclusion complexs with hydrophobic organic compounds.These processes occur in water,which is attractive as an environmentally benign solvent,which avoids the environmental pollution from organic solvents and metal catalysts.The reaction condition is mild and the operation is convenient and simple.In this thesis,we investigated the behavior of asymmetric reduction,oxidation, condensation in microreactor of cyclodextrins,the research results are as follows:1.Effects of substuent groups in the presence of microreactors of cyclodextrins on asymmetric reduction of acetophenone derivatives have been studied.The results indicated that substituent groups and low reaction temperature improved enantioselectivity for this asymmetric reaction.Absolute configuration of the resulting alcohols are depending upon the positions of substuent groups,preponderant absolute configuration of acetophenone and its meta- and para-derivatives was the S while the prevailing absolute configuration was the R in the case of the orth-derivatives.Effects of enantioselectivity of substituted acetophenones were due to the combination of bulkiness of substituent groups,hydrogen bonding,space steric hindrance and so on.In addition,preferential orientations of the substrate included inside the microreactor ofβ-cyclodextrin are suggested from above results.2.While the three-component inclusion complex is asymmetric reduced by the NaBH₄,the effect factors on asymmetric reduction of the acetophenone such as the kind of amides,molar ratio of theβ-Cyclodextrin/ketone/anime,temperature have been examine.Compared with binary system,the results indicated that cyclohexanamine enhanced chiral induction and inverted alcohol configuration.R(+)-1-phenylethanol was produced in 20%enantiometric excess for a molar ratioβ-CD:acetophenone:cyclohexanamine of 2:1:3,the reaction temperature is-5℃;the S(-) enantiomer in 6%enantiometric excess in the absence of cyclohexanamine.3.Chalcone and its derivatives are important organic intermediates. A new green method was studied for synthesis of Chalcones using microreactor of cyclodextrin as the inverse phase transfer catalysts and refluxed in water,the isolated yield was up to 90%.The method precludes the use of either strong base and product can be easily separated.The catalyst can be recycled with no pollution to the environment.4.Benzyl alcohol was oxidized to benzaldehyde under a mild condition in microreactor of cyclodextrins.The results showed that microreactor of cyclodextrins can be regarded as inverse efficient phase transfer catalysts for the oxidation of benzyl alcohol,this method is a direct one-pot synthesis under mild conditions,without pollution to the environment,the experimental steps are simple,cyclodextrins can be recovered and reused without loss of activity.Yield of benzaldehyde was up to 83.7%when the reaction temperature is 25℃,reaction time is 10 h, the molar ratio of theβ-cyclodextrin,benzyl Alcohol and NBS is 2:1:1.