Browsing by Author "Dr. Jonathan Lindsey, Committee Member"

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    Natural Product Synthesis via [2+2+2] Cyclotrimerization Reactions
    (2009-07-22) Teske, Jesse; Dr. David Shultz, Committee Member; Dr. Jonathan Lindsey, Committee Member; Dr. Daniel Comins, Committee Member; Dr. Alex Deiters, Committee Chair
    The transition metal mediated [2+2+2] cyclotrimerization reaction of alkynes is a highly convergent approach to the synthesis of polysubstituted carbo- and heterocyclic aromatic ring systems. However, few examples of the application of cyclotrimerization reactions in natural product synthesis have been reported. Here we explore the development of [2+2+2] cyclotrimerization reactions towards benzene derivatives applicable to the regioselective synthesis of indanone, isoquinoline, anthraquinone, cannabinoid, and neolignan based natural products. In addition, the development of [2+2+2] cyclotrimerization reactions towards pyridine derivatives applicable to the synthesis of the Streptomyces antitumor natural products streptonigrin and lavendamycin and several Lycopodium alkaloids has been explored. Optimization of the key cyclotrimerization events involved investigation of the alkyne (diyne or monoyne) and nitrile substitution pattern, the catalyst system employed, and conventional heating versus microwave irradiation.
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    Substituent Effects on Spin Density Distribution and Exchange Coupling in Semiquinone Complexes
    (2003-06-05) Sloop, Joseph C.; Dr. David A. Shultz, Committee Chair; Dr. Carl L. Bumgardner, Committee Co-Chair; Dr. Suzanne Purrington, Committee Member; Dr. Christopher Gorman, Committee Member; Dr. Jonathan Lindsey, Committee Member
    Design, synthesis, and characterization of novel high-spin species are critical in better understanding the field of molecular magnetism. It is also critical in advancing the field to a level of application, where new magnetic materials can be used in daily life. In this work, structure-property relationships of mono- and bis(semiquinone)s (SQs) were studied, substituent effects on exchange coupling and other physical properties were investigated, and a series of novel manganese(II), copper(II) and zinc complexes were synthesized and characterized. Within an isostructural series of SQs and their Manganese(II) and Copper(II) complexes, substituents were found to modulate reduction potentials, UV-visible absorption maxima and exchange coupling. This work represents the first examination of whether an empirical relationship exists between these physical properties of these radical anionic systems and Hammett sigma parameters. In a related investigation, SQ species with planar geometry and their Copper(II) complexes were prepared. Preliminary results indicate that substituent effects in these systems are nominal. Finally, three meta-phenylene-type (MPL), ferromagnetically coupled bis(SQ)s (substituents = H, Ph, OCH₃) were prepared to continue an earlier project which determined that both donating (NMe₂) and withdrawing (NO₂) groups attenuate the singlet-triplet gap (ΔEST) in the ground-state triplet species. A relatively simple Hückel molecular orbital explanation described the effect. It is the first time that a singlet-triplet gap (Λ[subscript ST]) of a ground-state triplet biradical has been affected by substituents. The results of this research were found to be consistent with earlier work.