摘要：

The thesis deals with the development of photoredox catalysis by visible light-mediated single-electron transfer reactions for application in synthetic organic chemistry.Chapter 1 represents a synopsis concerning the beginnings of organic photochemistry from a synthetic point of view. The discovery of the first chemical reactions driven by light are presented alongside their importance in biology (photosynthesis) and technical applications (photography). The section discusses accidentally discovered single photochemical reactions as well as the Ciamician's first systematic study on the behavior of light towards matter which led to the development of this new branch of chemistry. Moreover, chapter 1 highlights the discovery of certain basic physical principles which helped to explain the results and observations of early photochemical reactions.Chapter 2 describes the homogeneous Photo-Meerwein reaction, a visible light-driven intermolecular arylation of pi-electron donors by aryl radicals. Aryl radicals as the key intermediates were generated through photocatalytic one electron reduction of arenediazonium cations by redox active transition metal based and metal free chromophores as photocatalysts. Control Experiments confirmed the photocatalytic nature of the reaction. The Photo-Meerwein arylation was found to proceed through radical addition to unsaturated substrates, oxidation of the intermediate, and deprotonation to give the unsaturated arylated product. Investigations with respect to the substrate scope of the method showed high tolerance toward a multitude of functional groups. A large number of arene-diazonium salts was effectively coupled in the direct arylation of olefins, acetylenes, enones, and N heteroarenes. Further characteristics of this photo-catalytic C C coupling reaction include high yields, low catalyst loadings, and mild conditions.A heterogeneous Photo-Meerwein reaction is presented in chapter 3. Cellulose sheets were chemically modified by covalent attachment of coumarin as a chromophore to make the surface sensitive to the Photo-Meerwein conditions. The use of a mask to pattern the surface resulted in directly visible images and allowed spatial resolution throughout the photocatalyzed reaction, since arylation occurred only in irradiated parts and not in parts covered by the non-transparent photomask. Arylation altered the photophysical properties of the chromophore and led to an image observable with both spectroscopic methods and the naked eye.The last section (chapter 4) deals with a visible light mediated alpha-oxyamination reaction as a result of a one electron oxidation in the presence of [Ru(bpy)3]2+ (bpy = 2,2'- bipyridyl) as a photocatalyst. The required redox energy arose from the electronic excitation of the photocatalyst with visible light. 2,2,6,6 Tetra-methylpiperidine nitroxide (TEMPO) was found to be photocatalytically oxidized to the oxoammonium ion (TEMPO+) and was subsequently trapped by various nucleophiles to yield alpha-functionalized carbonyl compounds. The reaction time was significantly reduced by the use of microreactor technique.

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