ORCID Identifier(s)

0000-0001-6231-1451

Graduation Semester and Year

2019

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry

Department

Chemistry and Biochemistry

First Advisor

Alejandro Bugarin

Abstract

The triazene functional group has found numerous applications in organic and medicinal chemistry, with several important chemotherapeutic drugs containing this functionality. In spite of this, the reactivity of π-conjugated triazenes has been scarcely explored. The work described in this dissertation investigates the synthesis and new reactions of π-conjugated triazenes developed in our group, demonstrating the versatility of these molecules that allow access to several functionalities which can serve as building blocks for more complex structures. Chapter 1 surveys the prior literature of π-conjugated triazenes, describing their known synthesis and reactivity . In Chapter 2, new oxidation and substitution reactions of organic azides through the intermediacy of π-conjugated triazenes are discussed. Oxidation reactions are performed utilizing organic azides, imidazolium salts, and potassium tert-butoxide in DMSO to form a triazene intermediate, which readily undergoes oxidation under mild, acid-catalyzed conditions. Additionally, by replacing DMSO for other nucleophiles such as; alcohols or thiols, substitution reactions occur instead which generate ethers and thioethers respectively. Chapter 3 presents a transition-metal-free aryl-aryl cross-coupling reaction between π-conjugated triazenes and arenes or heteroarenes under UV irradiation (350 nm) in acidic conditions. The biaryls or heterobiaryls are obtained in a straightforward fashion at room temperature and in short reaction times. The reaction can also be performed using sunlight as radiation source. Computational studies suggest that the reaction proceeds through photoisomerization of the triazene to the Z-isomer which readily decomposes to produce a reactive aryl cation, which undergoes coupling with its corresponding (hetero)arene. Finally, in Chapter 4, the formation of amides by reacting aryl π-conjugated triazenes with nitriles under UV irradiation (350 nm) is described. Studies with isotopically labeled molecules suggest that the reaction involves nucleophilic attack by the nitrile nitrogen to an aryl cation derived from the arene. Due to the similarity in the reaction conditions with the aryl-aryl cross-coupling reaction introduced in the previous chapter, these two methods can be performed in one-pot, introducing both an amide as well as a biaryl group in the same step. This was demonstrated by synthesizing an immunosuppressant using this combined reaction, highlighting the potential synthetic utility of these transformations.

Keywords

π-conjugated triazenes, Azide oxidation, Azide substitution, Metal-free cross-coupling, Photochemical cross-coupling, Photochemical amide synthesis

Disciplines

Chemistry | Physical Sciences and Mathematics

Comments

Degree granted by The University of Texas at Arlington

Included in

Chemistry Commons

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