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Interrupted Nazarov reaction, allylic alcohol transposition, Nazarov reaction, electrocyclization, Alternative Nazarov reaction

Fradette, Ryan J

Supervisor and department: West, Frederick Chemistry

Examining committee member and department: Clive, Derrick Chemistry Gibbs-Davis, Julianne Chemistry Vasanthan, Thava Agricultural, Food and Nutritional Science Hall, Dennis Chemistry Floreancig, Paul Chemistry, University of Pittsburgh

Department: Department of Chemistry

Specialization:

Date accepted: 2014-08-26T09:36:26Z

Graduation date: 2014-11

Degree: Doctor of Philosophy

Degree level: Doctoral

Abstract: This dissertation expands the scope and understanding of the Nazarov electrocyclization and interception of the reactive cyclopentenyl cation intermediate that is formed though a 4π electrocyclization of a pentadienyl cation. An intermolecular process for interrupting the Nazarov is discussed. Also, a new class of alternative substrates, and a new method of activation is presented. Recent advances in the area of Nazarov chemistry is summarized in Chapter 1. Interrupting the Nazarov reaction from its typical pathway by trapping the reactive cyclopentenyl cation with a nucleophile, or the enolate intermediate with an electrophile enables rapid gains in molecular complexity. Alternative substrates and methods of activation can avoid some of the restrictions faced when using traditional acid activation of cross-conjugated ketones. Chapter 2 describes the Lewis acid mediated tandem Nazarov cyclization-intermolecular electrophilic aromatic substitution cascade. Our observations suggest that a diquinane is essential in establishing a cyclopentenyl cation that is sufficiently reactive and persistent to be trapped by the arene nucleophile. Importantly, complete regioselectivity and diastereofacial selectivity was observed for arene the trapping. An oxidation-initiated Nazarov cyclization of 1,4-pentadien-3-yl ethers was developed Chapter 3. The DDQ oxidation of the 1,4-pentadien-3-yl ether substrates led to a reactive pentadienyl cation intermediate that successfully underwent Nazarov cyclization. The process was terminated by a highly regioselective elimination to generate cyclopentadienol ethers bearing an exo methylene. The exo elimination was notable, leaving the two new stereocenters formed in the stereospecific cyclization step untouched. A facile 1,3-transposition of allylic alcohols that was previously observed while preparing substrates for the vinylogous Nazarov reaction has been studied. We were able to expand the scope of this method to include a variety of tertiary propargylic bisallylic alcohols, tertiary propargylic allylic alcohols, tertiary bispropargylic allylic alcohols, and bisallylic cyanohydrins Chapter 4. Additionally, the vanadium catalyzed transposition was carried out in tandem with a gold catalyzed cycloisomerization to generate tri-substituted furans.

Language: English

DOI: doi:10.7939-R3707WT63

Rights: Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.





Author: Fradette, Ryan J

Source: https://era.library.ualberta.ca/


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