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Seven- and Eight-Membered Ether Formation via Sulfonium Ylide Rearrangement Processes and Application in an Approach to (+)-Laurencin Open Access

Descriptions

Other title
Subject/Keyword
rearrangement
laurencin
synthesis
7- and 8-membered ether
sulfonium ylide
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Cao, Liya
Supervisor and department
Frederick G. West (Department of Chemistry)
Examining committee member and department
Liang Li (Department of Chemistry)
Jon D. Rainier (Organic Chemistry, University of Utah)
Dennis Hall (Department of Chemistry)
John M. Seubert (Pharmaceutical Sciences)
Christopher W. Cairo (Department of Chemistry)
Department
Department of Chemistry
Specialization

Date accepted
2010-02-02T17:15:36Z
Graduation date
2010-06
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
Given the large number of biologically active natural products containing medium-sized ether motifs, many organic chemists have shown great interest for developing new methodologies to access these structures. In particular, numerous synthetic methodologies for the construction of seven-membered and eight-membered ethers have been developed by research groups around the world. Recent advances in the synthesis of seven-membered and eight-membered ethers will be reviewed in chapter one. This chapter will cover some of the more notable publications from the last five years (from 2005 to 2009). In chapter two, the development of ring expansion reactions via [1,2]-shift rearrangements of thioacetal-derived sulfonium ylides will be described. A variety of functionalized diazoketones and diazoketoesters were made from commercially available starting materials. Sulfur-bridged seven-membered and eight-membered ethers were constructed upon treatment of these diazo precursors with suitable metal catalysts. It was found that Rh2(OAc)4 was a better catalyst for diazoketones, while Cu(hfacac)2 proved to be more effective for diazoketoesters. This methodology provides a convenient route to the seven- and eight-membered ethers in relatively few steps. In chapter three, the methodology for construction of sulfur-bridged ethers was employed as the key step in the attempted formal synthesis of (+)-laurencin. In this approach, the relative and absolute stereochemistry was established by a highly enantioselective and diastereoselective allylboration, a facially selective Michael addition, and a thermodynamically controlled acetal formation. The eight-membered sulfur-bridged ether was efficiently constructed using our [1,2]-shift reaction of a sulfonium ylide in toluene at 100 oC in the presence of Cu(hfacac)2. The following desulfurization and decarboxylation was effective at affording an advanced intermediate in this synthesis. The chemistry demonstrated in this chapter outlines a promising strategy for the formal synthesis of (+)-laurencin.
Language
English
DOI
doi:10.7939/R3KB0K
Rights
License granted by Liya Cao (lcao@ualberta.ca) on 2010-01-31T23:13:59Z (GMT): 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 the above terms. The author reserves all other publication and other rights in association with the copyright in the thesis, and except as herein 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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