Development of Visible Light-Promoted Photocatalytic O-Glycosylation, C-H Activation of Alkanes and Deoxygenation of N-(Mesyloxy) Amides

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

A stability condition for turbulence model: From EMMS model to EMMS-based turbulence model

The closure problem of turbulence is still a challenging issue in turbulence modeling. In this work, a stability condition is used to close turbulence. Specifically, we regard single-phase flow as a mixture of turbulent and non-turbulent fluids, separating the structure of turbulence. Subsequently, according to the picture of the turbulent eddy cascade, the energy contained in turbulent flow is decomposed into different parts and then quantified. A turbulence stability condition, similar to the principle of the energy-minimization multi-scale (EMMS) model for gas-solid systems, is formulated to close the dynamic constraint equations of turbulence, allowing the heterogeneous structural parameters of turbulence to be optimized. We call this model the `EMMS-based turbulence model', and use it to construct the corresponding turbulent viscosity coefficient. To validate the EMMS-based turbulence model, it is used to simulate two classical benchmark problems, lid-driven cavity flow and turbulent flow with forced convection in an empty room. The numerical results show that the EMMS-based turbulence model improves the accuracy of turbulence modeling due to it considers the principle of compromise in competition between viscosity and inertia.Comment: 26 pages, 13 figures, 2 table