Visible-Light-induced Photocatalytic Synthesis Of Indole Derivatives

The energy of visible light, for its clean and abundance, a variety of methods were developed to get use of this energy, and its utilization has gained widespread attention. Meanwhile, with the prosperous development of catalytic chemistry, visible light photocatalysis as a kind of catalytic processes have attracted great interests from synthetic organic chemists. Many elegent progresses have been made by some research groups, and the methodology has become a useful tool to design new reactions. It has already played a pivotal role in the accomplishment of synthetically useful transformations. In this dissertation, we describe the recent advances in the field of visible light photocatalysis. Employing the strategy of photocatalysis, we performed our research on the construction of diversely functionalized indole derivatives.First, based on the idea that the nitrene intermediate can be easily generated from azide compounds under visible light irradiation, we designed and synthesized various styryl azides. Subsequently, a visible-light-induced photocatalytic intramolecular cyclization of styryl azides has been developed in the presence of 0.5 mol% of Ru(bpy)3Cl2.6H2O as photocatalyst at room temperature through an energy transfer mechanism. The reaction is easy to handle and shows a wide substrate scope. The 2-substituted-N-free indole derivatives can be obtained in up to 99% isolated yields.In order to test the synthetic utility of our method, the reaction can be enlarged to gram scale, and changing the light source from 3 W white LEDs to sunlight do not affect the reaction efficiency. Moreover, based on the evidence of control experiments we proposed a possible reaction mechanism.Second, based on the previous work about energy transfer, we designed and synthesized a type of diazo compounds bearing electron-withdrawing groups, and accomplished their C-H functionalization ring closing to construct 3-ester oxindole derivatives. With the same photocatalyst the 3-hydroxyl-3-ester-2-oxindoles are further synthesized through aerobic oxidation of the 3-ester oxindole derivatives. This tandem reaction combines the energy transfer catalytic cycle and single electron transfer catalytic cycle, and provides an efficient access to various biologically important 3-hydroxyl-3-ester-2-oxindole dereivatives. Based on the experiment evidence and DFT calculation of the triplet energy of the substrates, we proposed a possible reaction mechanism of the phototandem reaction.Finally, based on our work on the indole synthesis through visible light photocatalysis and the previous work about the sulfur ylides, we designed and synthesized a kind of two electron-withdrawing-group stabled inert sulfur ylides, and accomplished their photocatalytic transformation. The transformation of this kind of sulfer ylides through visible light induced photocatalysis is reported by us for the first time. The key to success of the reaction is the single electron transfer between the stable sulfur ylide and photocatalyst. Employing this strategy, the process is proved to be thermodynamic favorable through the cyclic voltammetry calculation. A series of biologically important oxindole derivatives were synthesized in generally good yields.