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Title: Chiral guanidine catalyzed enantioselective protonation reactions
Keywords: Protonation,Isomerization,Atropisomerism,Kinetics,Guanidine,Enantioselectivity
Issue Date: 30-Nov-2009
Citation: LEOW DASHENG, JACKSON (2009-11-30). Chiral guanidine catalyzed enantioselective protonation reactions. ScholarBank@NUS Repository.
Abstract: The aim of this study is to develop highly enantioselective protonation reactions catalyzed by chiral bicyclic guanidine. Three reaction systems using both linear and cyclic substrates were presented. The first system is the enantioselective protonation of phthalimidoacrylates with thiols, with ees up to 94%. The second system is the enantioselective protonation of itaconimides with secondary phosphine oxides, with ees up to 99%. The last system developed is the enantioselective protonation of itaconimides with thiols, with ees up to 90%. Kinetic studies using NMR supports the postulated mechanism in which guanidine catalyst simultaneously activates itaconimide and secondary phosphine oxide through hydrogen-bonding from side-on approach. Chiral bicyclic guanidine is also found to catalyze the isomerization of alkynes to chiral allenes with high enantioselectivities. The axial chirality of the allenes is efficiently transferred to functionalized butenolides products.
Appears in Collections:Ph.D Theses (Open)

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