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Date of Award
Thesis-ISU Access Only
Master of Science (MS)
Department of Chemistry
Timothy A. Mitchell
Oxidopyrylium intermediates are dipolar, aromatic, zwitterions which have been shown to undergo cycloaddition in a concerted fashion with alkenes and alkynes to produce bridged bicyclic ethers. Oxidopyrylium-alkene [5+2] cycloadditions provide an efficient route towards the synthesis of complex three-dimensional ring systems. By investigating these systems we hope to allow these reactions to reach their full potential as a synthetic methodology. Initial investigations towards the development of a reliable methodology for enantioselective oxidopyrylium-alkene [5+2] cycloaddition have lead to a variety of projects probing fundamental reactivity of oxidopyrylium generation and cycloaddition processes.
Investigation of the unique reactivity difference of syn- and anti-acetoxypyranone diastereomers in oxidopyrylium-alkene [5+2] cycloadditions has shown a general trend in which syn-acetoxypyranones undergo conversion to bridged ethers at a qualitatively faster rate than anti-acetoxypyranones regardless of alkene substitution or reaction conditions. In addition, novel [5+2] cycloaddition conjugate addition cascade (C3) sequences derived from acetoxypyranone-alkenes with pendant nucleophiles were investigated which allow for the synthesis of tetracyclic ether cycloadducts with excellent diastereoselectivity in either a tandem or step-wise reaction sequence. Finally, we have explored the general utility of acid-mediated oxidopyrylium activation of pyranones. While screening of various acid mediators in a model reaction revealed limited efficiency, reactivity studies provide data that not only shed light on acid-mediated activation but also thermal- and base-mediated processes.
Simanis, Justin Adam, "Fundamental Investigations of Pyranone Activation to Oxidopyrylium Intermediates and Corresponding [ 5 +2 ] Cycloaddition Processes" (2014). Theses and Dissertations. 226.
Available for download on Sunday, October 13, 2024