Theoretical Study On Several Synthesis Reactions Catalyzed By The Imidazolidinone Catalyst

The asymmetry reactions catalyzed by the imidazolidinone catalyst play animportant role in organocatalysis chemistry. In this thesis, the reaction mechanismsand the potential energy surfaces of several asymmetry reaction catalyzed byimidazolidinone catalyst have been explored using density functional theory methods.The reaction mechanism and some important information such as geometries andenergies of the reactant, intermediates, transition states and products are obtained. Onthe basis of the relation of the reactant, intermediates, transition states and products,the possible reaction channels as well as the enantioselectivity also provided. Theresults obtained in this thesis are compared with previous experimental findings andmay shed some light on the future experimental investigations of these kinds ofreactions. The main results are summarized as follows:1. The intramolecular asymmetric Michael addition reaction catalyzed byimidazolidinone is investigated using the density functional theory calculations. Thedetails of the reaction mechanism, potential energy surfaces, and the influence of theacid additive are investigated. The reaction process includes two stages. The firststage is Michael addition, in which the enamine complex is created and then theMichael addition is carried out. The second stage is a product separation stage whichincludes an enol-keto tautomerization and a two-step hydrolysis. Theenantioselectivity is controlled by the Michael addition step which involves a newcarbon-carbon bond formation. The calculation results provide a general model whichmay explain the mechanism and enantioselectivity of the title reaction.2. The Friedel–Crasfts alkylation reaction of α, β-unsaturated butyric aldehydeswith N, N-dimethyl-3-anisidinecatalyzed by a (2S,5S)-5-benzyl-2-tert-butyl-3-methylimidazolidin-4-one HCl salt have been carriedout at the PCM(CH2Cl2)/B3LYP/6-311++G(d,p)//B3LYP/6-31G(d) level. Threereaction processes have been characterized:(I) the formation of an iminium ionintermediate;(II) the1,4-iminium addition of the iminium ion; and (III) thehydrolysis of the addition product. Moreover, Path1-1is the favorable channel in theformation of the iminium ion. From the point of view of energy, the enantioselectivityis controlled by the carbon–carbon bond formation step that is involved in both theintermediate M4and the transition state TS4. The highest energy barrier of thereaction is the H2proton transfer from the O10atom of a water molecule to the N1atom of the catalyst in the hydrolysis process, which is23.4kcal/mol. The presentedcalculated results may be helpful in understanding the experimental productdistribution for the title reaction, and provide a general model to help explain themechanisms of similar reactions.3. The cascade reaction of α, β-unsaturated butyric aldehyde with2-methyl furanand chlorinated quinine catalyzed by a (2S,5S)-5-benzyl-2-tert-butyl-3-methylimidazolidin-4-one TFA is investigated by usingdensity functional theory (DFT) calculations at the PCM(EtOAc)/B3LYP/6-311++G(d,p)//B3LYP/6-31G(d) level, to (I) confirm the detailed reaction mechanism and keyfactors controlling the enantioselectivity, and (II) check the models of iminium ionformation and hydrolysis process that constructed in another reaction. Two favorablereaction channels, corresponding to the enantioselectivity of (2R,3S)-product and (2S,3S)-product, have been characterized. The enantioselectivity is controlled by the stepsinvolved in the formation of C-C bond and C-Cl bond in the iminium catalysis andenamine catalysis, respectively. The calculated results explain the reaction mechanismand the enantioselectivity which in agreement with experimental observations, andmay be helpful to understand the reaction mechanism of similar cascade reactions.