New Developments in Platinum-Catalyzed Cyclization and Fluorination of Polyenes Public Deposited

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  • March 22, 2019
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  • Cochrane, Nikki Alsop
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • This dissertation encompasses two major components, both focused around the platinum(II) catalyzed cyclization of polyenes into polycyclic compounds. Previous studies have determined that in the Wacker-type platinum(II) catalyzed net dehydrogenative cyclization reactions, [Pt]-H is stable towards elimination, making typical 2-electron oxidants ineffective in these systems. As a result, Ph3C+ was used to abstract hydride from the [Pt]-H resulting in triphenylmethane and turning over the catalytic cycle. There are many inherent problems using Ph3C+, in particular, the steric bulk and cumbersome workup. For this reason, this dissertation focuses on exploring alternative turnover mechanisms for these platinum(II) cascade cyclization reactions of polyenes. The first project focuses on the development of a system with a hydride abstractor that is more atom economical than Ph3C+ and can provide facile workup procedures. We found that dimethoxymethane, although slower, performed as well as Ph3COMe. In addition, dimethoxymethane suppressed the formation of byproducts and was easily removed during product isolation. Also described in this thesis is the development of a platinum(II) catalyzed enantioselective cyclization/fluorination reaction for formation of C-F bonds in polycyclic compounds. After extensive optimization, it was discovered that a bidentate phosphine ligand, (S)-(xylyl-phanephos), can generate the desired bicyclic product in approximately 70% yield with enantioselectivities as high as 87%. We propose that the platinum(II) catalyzed cyclization/fluorination proceeds through electrophilic fluorine addition to a [Pt]II-alkyl complex resulting in a putative [Pt]IV-F species. As this platinum (IV) species has never been observed in our catalytic system, we sought to develop a model [Pt]IV-F complex to investigate its viability as a catalytic intermediate. Initial studies have indicated the formation of a [Pt]-F species, but its identity has not yet been determined.
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  • In Copyright
Advisor
  • Gagne, Michel
Degree
  • Doctor of Philosophy
Graduation year
  • 2013
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