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Permanent link (DOI): https://doi.org/10.7939/R3H991

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Oxonium Ylide Rearrangements: A Novel Approach Towards the Synthesis of the Phorbol Skeleton Open Access

Descriptions

Other title
Subject/Keyword
Phorbol
Stevens Rearrangement
Oxonium Ylide
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Stewart, Craig
Supervisor and department
West, Frederick, G. (Chemistry)
Examining committee member and department
Cowie, Martin (Chemistry)
Clark, Stephen, J. (University of Glasgow, Chemistry)
Mercer, John (Oncology)
Lowary, Todd, L. (Chemistry)
Clive, Derrick, L. J. (Chemistry)
Department
Department of Chemistry
Specialization

Date accepted
2010-01-28T15:54:07Z
Graduation date
2010-06
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
Oxonium ylides are highly reactive intermediates that can be used for the synthesis of heterocyclic and carbocyclic frameworks. These putative intermediates are almost exclusively formed from diazocarbonyl derived metallocarbenes, by attack of a pendent oxygen atom. Oxonium ylides have been shown to furnish products derived from the [1,2]-shift (Stevens rearrangement) or the [2,3]-shift in an efficient manner. Chapter 1 is a review of oxonium ylides in synthesis focusing on factors that influence the reactivity of these intermediates. Previous work has shown that the sulfur-directed Stevens rearrangement is an efficient reaction for the generation of seven and eight-membered oxa-bridged carbocycles fused to five-membered rings. Chapter 2 describes an extension of this chemistry where six-seven and six-eight membered oxa-bridged carbocyclic products were furnished in good yields. The chemo- and diastereoselectivity of these rearrangements was dependent on the configuration of the acetal stereocentre present in the diazoketone precursor. A novel approach towards the synthesis of the tigliane and daphnane diterpenes is described in Chapter 3. The tricyclic framework was generated from a highly stereoselective oxygen-directed Stevens rearrangement of an oxonium ylide. This methodology provides a straightforward route to the construction of the five-seven-six ring system found in these classes of natural products. Finally, the sulfur-directed Stevens [1,2]-shift was employed in an attempted total synthesis of the natural product (+)-phorbol in Chapter 4. Several variations of the original synthetic scheme were examined, in an effort to construct the core 6-7 ring structure. The Stevens rearrangement was found to provide the 6-7 ring system of phorbol in excellent yield. The chemo- and diastereoselectivity of this rearrangement was dependent on the configuration of the acetal centre as well as the conformation of the six-membered ring in the starting material. In the future, this advanced intermediate could be used to achieve the total synthesis of (+)-phorbol.
Language
English
DOI
doi:10.7939/R3H991
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. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. 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.
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