New flavins and their application to chemical photocatalysis

The presented dissertation comprises the synthesis of substituted flavins and their application as photocatalysts. Chapter 1 contains a short introduction into possible redox states of flavins, especially under light irradiation and previous applications of flavin-based photocatalysts in particular of our working group are presented. The synthesis of various flavin-thiourea derivatives is described in chapter 2. These compounds and mixtures of flavins with thiourea were successfully applied to the photooxidation of 4-methoxybenzyl alcohol. High conversions were achieved with such catalytic systems and also the use in preparative experiments. However, in water as reaction media, the reaction proceeds faster and with increased efficiency. In contrast to reactions in acetonitrile, also non activated benzyl alcohols can be oxidized. Chapter 3 contains the experiments in water and the immobilization of flavins on solid support or in polyethylene. Simple separation from the reaction mixture and possible recycling make these catalysts valuable for application, however, showing the same reactivity compared to homogeneous solution. Templated flavins were synthesized by fixing the chromophore together with a substrate binding site on a platform (chapter 4). Such assemblies increase the probability for a photoinduced electron transfer reaction, therefore optimizing the reactivity of flavins under light irradiation. A novel synthetic approach to 3-N-arylation by reaction with phenyl boronic acids is presented in chapter 5. For the first time, this method enables a direct coupling of aromatic systems to the 3-N-position of a flavin. Terminatory, chapter 6 contains the synthesis of a new diamin derived from Kemp´s Acid. This easily accessible rigid platform makes the composition of structurally defined compositions feasible