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Browsing by Author "Ferreira, Eric, advisor"

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    The formation and reactivity of α,β-unsaturated platinum carbenes: new approaches to heterocycle synthesis
    (Colorado State University. Libraries, 2014) Allegretti, Paul Andrew, author; Ferreira, Eric, advisor; Rovis, Tomislav, committee member; Kennan, Alan, committee member; Elliott, C. Michael, committee member; Crick, Dean, committee member
    The use of transition metal carbenes in organic synthesis has enabled chemists to promote an incredible variety of bond-forming reactions. These intermediates are traditionally accessed via the decomposition of diazo species. Alternative methods for accessing metal carbene intermediates from functional groups beyond diazo species could present many practical advantages and would complement the existing methods. Presented herein are our efforts to develop a novel method of carbene generation from the reactions of alkynes and π-acidic transition metals, and their use in the synthesis of different heterocycles. Our initial investigations focused on the ability to generate substituted furan products from the intramolecular addition of alcohols into alkynes containing propargylic methyl ethers. We then extended this reaction manifold to the synthesis of complementary positional isomers of isoxazoles, adding both propargylic N-hydroxycarbamates and propargylic N-Boc amino ethers into the activated alkyne. Key to this transformation was the inclusion of Brønsted acids to facilitate activation and elimination of the methyl ether leaving group. While studying the synthesis of furans and isoxazoles it was observed that the nature of the carbene could be modulated, leading to selective silicon or hydrogen migration. Also observed was the addition of nucleophiles into the β-position of the carbene species. This last mode of reactivity led to the discovery of a new way to synthesize vicinal bisheterocycles using alkyne activation conditions.
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    Utilizing silicon for the synthesis of tri- and tetrasubstituted olefins
    (Colorado State University. Libraries, 2013) Rooke, Douglas Alexander, author; Ferreira, Eric, advisor; Wood, John, committee member; Fisk, John D., committee member; Shores, Matthew, committee member; Peersen, Olve, committee member
    Functionalized organosilanes serve an important role as reactive precursors for a number of synthetic transformations. Consequently there is still great use for the development of new methods that allow for facile and efficient generation of organosilicon compounds. Herein, a number of such methods are described. The stereoselective syntheses of α-silylenones using catalytic PtCl2 are reported. Via alkyne activation, α-hydroxypropargylsilanes are converted to (Z)-silylenones through a highly selective silicon migration. A trans halosilylation of alkynes is also reported. Both the PtCl2 catalyzed silyl migration the halosilylation reaction proceed through a 1,2-silicon shift onto the activated alkyne intermediate in an anti fashion relative to the activating agent. Both reactions afford excellent yields and selectivity for the product tri- and tetrasubstituted alkenes. The high yielding Pt catalyzed hydrosilylation reactions of internal alkynes are described with a focus on understanding the factors that govern the regioselectivity of the process. Electronic, steric, and functional group properties all influence the selectivity, an understanding of which allows the selective formation of trisubstituted vinylsilanes, which are synthetically useful compounds for accessing stereodefined alkenes. Finally, efforts to show the synthetic utility of tri- and tetrasubstituted vinylsilanes for the formation of C-C bonds using Hiyama coupling and halodesilylation reactions are reported. Hiyama couplings of tetraorganosilanes with and without the use of fluoride activators are thoroughly evaluated. Coupling reactions with vinylsiloxanes are also shown. Finally, stereoretentive halodesilylation reactions are explored with the product vinylhalides subsequently subjected to Suzuki cross coupling conditions affording high yields of highly substituted all-carbon alkenes with good retention of alkene geometry.