Vinylogous Michael cascade reactions employing silyl glyoxylates and silyl glyoximides

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  • March 21, 2019
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  • Boyce, Gregory Ronald
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • I. Vinylation-Initiated Vinylogous Michael Cascade of Silyl Glyoxylates and Elaboration to Nitrocyclopentanols: An investigation of the reaction parameters required to achieve a vinylation-initiated vinylogous Michael cascade of silyl glyoxylates and nitroalkenes was performed. The reaction achieved the (Z)-enol silane products with complete regio- and diastereoselectivity. A rationale for the high levels of selectivity is discussed. Discussion of how the probable mechanism of the three-component coupling was discerned (vinylogous Michael, [3,3] rearrangement, or Diels-Alder type pathway) is presented. This method provides an easily accessible synthetic equivalent to the unusual a-keto ester homoenolate. These (Z)-enol silane products were further elaborated to nitrocyclopentanols via a highly diastereoselective Henry cyclization. Rationale for the diastereoselectivity is presented as well as an analysis of this methodology's impact compared to other methods for highly substituted nitrocyclopentanols is also presented. II. Alkynylation-Initiated Vinylogous Michael Reaction of Silyl Glyoxylates and Elaboration to Cyclopentanol Derivatives: An investigation of the reaction parameters necessary to accomplish an alkynylation-initiated Kuwajima-Reich/vinylogous Michael cascade of silyl glyoxylates and nitroalkenes is presented. The title three-component coupling provided tetrasubstituted silyloxyallenes with high levels of regio- and diastereoselectivity. The impressive selectivity of this transformation was investigated through a quantum mechanical study using the density functional theory approach at the level of B3LYP/6-311G(d). This study corroborated previous studies on the identity of the transient secondary nucleophile as the (Z)-glycolate enolate and provided a rationale for the excellent diastereoselectivity observed through nitro group coordination to the (Z)-glycolate enolate. A discussion of the additional empirical studies performed to confirm the proposed mechanism is also presented. The tetrasubstituted silyloxyallene products were then derivatized to cyclopentenols and cyclopentitols. III. Silyl Glyoximides as Asymmetric Conjunctive Reagents Through Long-Range Stereoinduction: The utility of silyl glyoximides as a new class of asymmetric conjunctive reagents in the vinylation-initiated vinylogous Michael cascade with vinyl Grignard and nitroalkenes is presented. The reaction affords the desired gamma-adducts with excellent regio-and diastereoselectivity. A rationale for this long range stereochemical transmission is proposed. A discussion of the benefits of silyl glyoximides compared to silyl glyoxylates in terms of the current methodology is presented. Initial studies towards the various Henry cyclizations are also presented.
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  • In Copyright
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  • "...in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Chemistry."
Advisor
  • Johnson, Jeffrey
Degree granting institution
  • University of North Carolina at Chapel Hill
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Place of publication
  • Chapel Hill, NC
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  • Open access
Date uploaded
  • March 18, 2013

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