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Study of rotationally restricted systems and synthesis of acridinium photocatalysts

Zilate, Bouthayna. Study of rotationally restricted systems and synthesis of acridinium photocatalysts. 2020, Doctoral Thesis, University of Basel, Faculty of Science.

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Official URL: http://edoc.unibas.ch/diss/DissB_13713

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Abstract

Stereoselective organocatalyzed transformations involving rotationally restricted systems
Stereoselective organocatalyzed reactions are powerful synthetic tools complementary to transition metal-catalyzed transformations that allow access to a large variety of chiral scaffolds with stereogenic centers, axes or planes. Due to their low toxicity and ready availability, small molecule catalysts represent thus a more sustainable alternative for the synthesis of complex structures.
Herein we investigated an enantiospecific electrophilic substitution catalyzed by orthosubstituted anilines through the formation of atropisomeric enamine intermediates. Using an enantiopure a-fluorinated aldehyde as a substrate, several anilines bearing bulky orthosubstituents were tested to selectively catalyze the addition of an electrophile to form a quaternary stereocenter with retention or inversion of configuration.
Multi-axis systems with rotationally restricted bonds are topologically well-defined motifs and valuable chiral scaffolds with diverse applications from catalysis to medicinal chemistry. However, synthetic pathways to these compounds as well as studies about their rotational behavior remain scarce. Therefore, we reported the enantioselective synthesis of rotationally restricted aromatic amides displaying three stereogenic axes. Catalyzed by a chiral tetrazole derived proline, the anilides were obtained with an e.r. up to 87:13 and a cis/trans ratio of 1:3. An exhaustive study was conducted to identify the 3D structures of the major compounds and to deepen our understanding regarding their rotational behavior.
Due to their peculiar handle-shaped structure imparting them a stereogenic plane, cyclophanes have always been a fascination for chemists around the world. Widely spread among natural products and bioactive compounds, they also find application in nanotechnologies and material sciences. If multiple synthetic strategy to access such macrocycles have already been described, the development of organocatalyzed transformation to obtain enantiopure cyclophanes is severely limited. Hence, we explored the use of the enantioselective arene forming aldol condensation developed in our group to achieve the synthesis of enantiopure paracyclophanes with an anthracene core and fifteen methylene groups on the side chain.
Synthesis of acridinium salts and their application in photoredox catalysis
The continuous development of photocatalytic methods motivates the design of organic catalysts towards a more sustainable approach, in order to complement the frequently used and precious polypyridyl transition metal complexes. However, this rational design is often hampered by the mechanistic complexity and low modularity of the catalyst structure. Herein, a scalable synthesis of symmetric acridinium dyes was reported. Optimized reaction
conditions and purification methods allowed to prepare these catalysts on multi-gram scale, using a double halogen-metal exchanged as a key step.
A thorough photophysical study of a diverging photocatalytic pathway drove the design and fully modular synthesis of asymmetric acridinium catalysts. A combination of halogen-metal exchange with directed ortho-metalation allowed to generate a wide panel of dyes with fine-tuned photophysical and photochemical properties.
Given the high degradation observed for several dyes during a photocatalytic reaction, the design of a new generation of photostable acridinium salts was tackled. Symmetric photocatalyst with carbazole moieties and asymmetric ones with a methoxy group on one side and a diphenylamino group on the other side of the core were thus synthesized.
Advisors:Sparr, Christof and Seebeck, Florian Peter and Juríček, Michal
Faculties and Departments:05 Faculty of Science > Departement Chemie > Chemie > Organische Chemie (Sparr)
UniBasel Contributors:Zilate, Bouthayna and Sparr, Christof and Seebeck, Florian Peter and Juricek, Michal
Item Type:Thesis
Thesis Subtype:Doctoral Thesis
Thesis no:13713
Thesis status:Complete
Number of Pages:1 Online-Ressource (IX, 256 Seiten)
Language:English
Identification Number:
Last Modified:13 Oct 2020 04:30
Deposited On:12 Oct 2020 12:32

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