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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Investigations Into Carbon Nanotube And Natural Product Synthesis.

Giampa, Geoffrey 01 January 2016 (has links)
This dissertation describes research into the synthesis of carbon nanotubes using traditional organic synthetic methods, as well as work on the fragmentation of β-hydroxy-α-diazoesters with a γ-hetero group and applications of their reactivity towards natural product synthesis. Carbon nanotubes are unique structures that can exhibit different electronic properties based on their chiral vector, and are a potential future source of semiconductors. Current methods of synthesis are unable to be adapted to commercial synthesis, providing the opportunity for the application of organic synthetic methods to generate them more uniformly and on a larger scale. The generation of tethered aldehyde ynoates and their utilization in 1,3-dipolar cycloadditions has been well developed by the Brewer group. Traditionally they have been generated from γ-siloxy-β-hydroxy-α-diazoesters, herein we explore utilizing an amino group as the fragmentation initializer. Additionally, application of the tethered aldehyde ynoate towards the synthesis of the natural products Demissidine and Aspidospermine are discussed.
2

Application Of A Ring Fragmentation/azomethine Ylide 1,3-Dipolar Cycloaddition Sequence In The Synthesis Of Demissidine

Zhang, Zhe 01 January 2014 (has links)
Edible potatoes originated in the Andes and were brought to Europe in the 16th century. Their introduction spurred both the European population growth and economic development. Being the world's fourth-largest food crop, potatoes continue to shape the global economy and world history. Glycoalkaloids are natural insect deterrents generated by potatoes, and are known for their toxic effects as well as potential medicinal utilities. Demissidine, the aglycone of the primary glycoalkaloids, represents one major Solanum alkaloid. Its unique indolizidine framework presents a challenging synthetic target in organic chemistry. Our synthesis of demissidine starts from readily available epiandrosterone and takes advantage of a Lewis acid-mediated fragmentation of a γ-silyloxy-β-hydroxy-α-diazoester; the D-ring of a diazo ester derivative of epiandrosterone was efficiently ruptured to provide an aldehyde tethered ynoate product. In combination with a subsequent azomethine ylide 1,3-dipolar cycloaddition and a transition metal catalyzed oxidation/reduction, the core indolizidine framework of demissidine was successfully prepared in a stereoselective manner. In addition, the syntheses of two amino acids, 5-methylenepipecolic acid and (5S)-5-methylpipecolic acid were explored; they are used for the installation of the α-oriented C25 methyl group on demissidine. The successful preparation of demissidine was supported by NMR analysis of the synthetic compound in comparison with a natural sample. As an efficient and stereoselective synthesis, our efforts toward demissidine illuminate a strategy to indolizidine frameworks that could be applied in the preparation of other polycyclic amine natural products.

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