Visible Light-Mediated Metal-Free Photocatalytic Oxidative Reactions and Cycloadditions

by Yu Zhang
Doctoral thesis
Date of Examination:2020-11-03
Date of issue:2020-11-16
Advisor:Prof. Dr. Konrad Koszinowski
Referee:Prof. Dr. Konrad Koszinowski
Referee:Prof. Dr. Shoubhik Das
Referee:Dr. Michael John
Referee:Prof. Dr. Dietmar Stalke
Referee:Prof. Dr. Bert Maes
Referee:Prof. Dr. Meynen Vera
Persistent Address: http://dx.doi.org/10.53846/goediss-8309

 

 

Files in this item

Name:thesis.pdf
Size:22.5Mb
Format:PDF

The following license files are associated with this item:

Abstract

English

Currently, there is a strong demand for the development of sustainable chemistry by reducing hazardous substances and using less energy during the process. Hence, ‘Green Chemistry’ or ‘Sustainable Chemistry’ has become the key research topic. Recently, visible-light-mediated organic syntheses experienced a blooming renaissance due to their numerous strengths compared to UV-light mediated reactions and thermochemical reactions. Parallel to this, development of solar-energy mediated organic transformation is also highly attractive for the augmentation of sustainable approach in the organic synthesis. Hence, we aimed to develop novel and green photocatalytic systems to achieve the highly valuable compounds with the current ongoing developments in visible-light photocatalysis. Firstly, visible-light-mediated oxygenation of tertiary amines has been achieved using rose bengal as a cheap and commercially available metal-free catalyst and produced water as the sole by-product. Besides the excellent substrates scope for small molecules, we also applied this mild photocatalytic system for the late-stage modifications of existing natural products and pharmaceuticals. Afterwards, a heterogeneous catalytic system with molecular oxygen as an oxidant was designed and employed under mild reaction conditions using nitrogen deficient graphitic carbon nitride as a heterogeneous catalyst. Versatile benzylic oxygenation/hydroxylation reactions afforded moderate to excellent isolated yield. More importantly, the reaction can progress even under the irradiation of cleaner and greener sunlight with good yields. Then we applied polymeric carbon nitrides (PCN) as a photocatalyst to develop the selective cleavage of C=C bonds in aryl olefins. This method was selective, scalable under the irradiation of sunlight and the photocatalyst was easily recyclable. In addition, we have been able to perform the late-stage cleavage of C=C bonds in aryl olefins to achieve highly valuable products and pharmaceuticals. The stability of PCN has been well investigated by different spectroscopic analyses. At last, we have used 9-fluorenone as a metal-free photocatalyst for the visible-light-mediated cycloaddition reactions which has proven to be an efficient, sustainable and metal-free possibility to synthesize cyclohexene derivatives. In addition, these mild conditions can be employed to synthesize bioactive 2,3-dihydropyridin-4(1)-one derivatives via aza-Diels-Alder reactions.
Keywords: Green Chemistry; Homogeneous photocatalysis; Heterogeneous photocatalysis; Oxidative reactions; Cycloadditions
 
Statistik