Master of Science (MS)
This thesis is divided into four chapters reporting various aspects of the background of studies and the preliminary results I obtained in three projects. Chapter 1 gives a brief introduction to the concepts of photoredox catalysis, O-glycosylation, C-H functionalization and amidyl radicals. Chapter 2 describes the development of a visible light-promoted O-glycosylation catalyzed by Ru(bpy)3(PF6)2 or diphenyldiselenide under mild conditions. The glycosylation of primary and secondary alcohols with selenoglycosides was demonstrated with good yields, and disaccharides were constructed by coupling of the selenoglycosides in acetonitrile or dichloromethane with a glucosyl acceptor in moderate yields. The reactions catalyzed by Ru(bpy)3(PF6)2 were fast and yielded moderate stereoselectivity, whereas the diphenyldiselenide-catalyzed reactions took extended time while the stereoselectivity was increased in less polar solvents. We also found that the choice of solvents had a marked effect on the stereoselectivity. Chapter 3 introduces the development of visible light-promoted photocatalytic C-H functionalization of alkanes. Two types of C-H activation, hydroxylation and amidation of adamantane, were demonstrated in the presence of transition metal polypyridyl photocatalysts, radical precursors, and nucleophiles (H2O or nitriles + H2O) under blue LED irradiation. Different photocatalysts, solvents, and substrate loadings were examined to optimize the reaction conditions. Side-reactions leading to low yielding of these photocatalytic C-H functionalization reactions were also examined. Chapter 4 discusses the importance of the amidyl radical in heterocycle construction and remote functionalization. A novel method to produce amidyl radicals by photocatalytic reduction of N-mesyloxy amides was proposed. This original concept was demonstrated by the photocatalytic deoxygenation of N-methyl-N-mesyloxy-4-phenylbutyramide in the presence of 1 mol% Ir(ppy)3 as photocatalyst, 2 equiv. diisopropylamine as terminal reducing agent and acetonitrile as solvent under blue LED irradiation. This novel method of generating amidyl radicals will be further exploited by my successor, Ms. Rashanique Quarels, to apply to heterocyclization and remote functionalization reactions.
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Wang, Xiaoping, "Development of Visible Light-Promoted Photocatalytic O-Glycosylation, C-H Activation of Alkanes and Deoxygenation of N-(Mesyloxy) Amides" (2014). LSU Master's Theses. 187.