Synthesis of Functionalized Benzenoid Macrocycles: An Approach to Accessing Functionalized Cycloparaphenylenes
Type of DegreeMaster's Thesis
Chemistry and Biochemistry
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Carbon nanotubes (CNTs) are cylindrically shaped allotropes of carbon with exceptionally good electronic and optical properties. The current state of art for making these CNTs involves heating graphite in a high temperature furnace (above 600 °C). The use of harsh temperatures makes the process unselective and produces CNTs as an inseparable mixture of products. Currently, there is no efficient purification technique for isolating pure CNTs. In order to fully exploit the electronic properties of CNTs, they need to be made as homogeneous and monodispersed structures. Thus, synthetic chemists envisioned using chemical synthesis from the ground-up via a template strategy as a more viable approach to achieve the selective synthesis of uniform CNTs structures with a defined chirality and diameter. This is because the selective synthesis of curved PAHs like [n]ciruclenes and CNT substructures could only be accomplished through chemical synthesis. The work described herein focuses on a new approach to accessing highly distorted p-phenylenes, which does not rely on cross coupling reactions and the use of the Burgess reagent as a mild dehydrative aromatization agent, giving access to highly strained benzenoid macrocycles. Chapter 1: A definition of CNTs, types of CNTs and their properties. A description of the industrial processes used in the synthesis of CNTs and their limitations. The selective synthesis of some curved PAHs like [n]circulenes and CNT substructures is described to illustrate the power of chemical synthesis in achieving challenging targets. Chapter 2: A template approach to the synthesis of uniform, single chirality CNT is described. Various approaches to CPP synthesis have equally been covered as well as the current limitation in the field. A non-cross-coupling approach to bent paraphenylenes have been described, as well as arene bridging strategy tolerable to ortho substitutents. Moreover, the use of the Burgess reagent as a powerful dehydrative aromatizing agent to achieve highly distorted paraphenylene and prevent rearrangements is demonstrated. Furthermore, a streamlined approach to access gram quantities of macrocyclic 1,4-diketones from acyclic dialdehydes has been developed which uses mild hydrogenation source, which has provided access to a wide variety of targets not accessible by other methods. Chapter 3: The synthesis of functionalized benzenoid macrocycles with ortho substituents is undertaken and progress towards converting them into functionalized CPPs is reported.