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SYNTHESIS OF PYRIDINIUM SALTS VIA NOVEL OXIDATIVE C-H FUNCTIONALIZATION METHODS

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Thesis/Dissertation
Date
2024-08
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Department
Chemistry
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DOI
http://dx.doi.org/10.34944/dspace/10603
Abstract
Pyridinium salts are scaffolds of diverse biological and synthetic importance. Thesemolecules can serve as oxidants, ionic liquids, phase transfer catalysts, and can be used as synthetic intermediates in a variety of complex chemical reactions. A limitation in the chemistry of pyridinium salts is the need for expensive reagents and forcing conditions for their synthesis from primary amines and alkyl halides. In chapter 1, a summary of recent methods for the synthesis of N-aryl pyridinium salts, as well as their synthetic applications is provided. This thesis focused on the development of novel strategies for the synthesis of pyridinium salts directly from C–H bonds. The first method, described in chapter 2, is the synthesis of N-aryl pyridinium salts using hypervalent iodine chemistry to access electrophilic arene radical cations which can be trapped by pyridine. This method represents a mild, environmentally friendly, and cost-effective alternative to existing oxidation methods which use expensive and toxic reagents. These resulting pyridinium salts can be easily converted to free amines or substituted piperidines. The second method, described in chapter 3, showcases a novel, serendipitously discovered reaction of quinoline derivatives in the presence of N-HVI reagents. This reactivity enables rapid access to a variety of aminoquinoline derivatives. Preexisting methods for the synthesis of The mechanism of this unique reaction was explored with a collaborative computational investigation. The resulting work led to a rapid synthesis of a variety of 2- and 4- aminoquinoline isomers. The third project, an electrochemical synthesis of N-benzyl collidinium salts, is detailed in chapter 4. Electrochemistry allows for unprecedented reactivity without the need for any external chemical oxidants in the reaction. The use of electrochemical oxidation enabled a broad scope that would have been challenging to access through the use of hypervalent iodine chemistry. The resultant collidinium salts were shown to engage in photoredox Giese reactions with acrylonitrile. The use of electrochemistry in this project has created new opportunities and strategies for the synthesis of pyridinium salts within the Wengryniuk lab.
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