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Authors: CHO BOKUN
Keywords: DFT, Organocatalyst, Kinetics, Enantioselectivity, Lewis acid, bicyclic guanidine
Issue Date: 28-Jul-2011
Citation: CHO BOKUN (2011-07-28). DFT STUDIES OF ORGANOCATALYZED REACTIONS. ScholarBank@NUS Repository.
Abstract: Asymmetric organocatalysis is one of the most robust methods in generating chiral molecules for the pharmaceutical industry with the process having low toxicity and ease of application in large scale synthesis. This thesis focuses on using DFT theoretical studies to elucidate the mechanism of organocatalyzed asymmetric reactions and account for the factors influencing the kinetics through the study of the transition states. The effect of the substituents on the thiourea catalyst in the Brønsted acid catalyzed Diels-Alder reaction is explored. The role of the sulphur-phenyl hydrogen bond within the catalyst on the activation of the reactants is also examined. Investigation of the phospha-Michael reaction mechanism has shown that the bifunctionality of the bicyclic guanidine catalyst is involved in all 3 stages of the reaction. The enantioselectivity is controlled by steric restriction of the catalyst on both reactants. Optimization of the catalyst is proposed by utilizing the transition states and kinetics of the original reaction. In the catalyzed thio-Michael reaction, the protonated guanidinium employs a unique bifunctional Lewis and Brønsted acid activation of the reactants to achieve the desired enantioselective product. The dimerization of the bicyclic guanidine enables an alternate route of catalysis which is kinetically preferred over the guanidine monomer catalyzed phospha-Michael reaction between itaconimides and diaryl-phosphine oxides.
Appears in Collections:Ph.D Theses (Open)

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