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Graduation Term


Document Type

Thesis-ISU Access Only

Degree Name

Master of Science (MS)


Department of Chemistry

Committee Chair

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.


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