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Permanent link (DOI): https://doi.org/10.7939/R3494Q

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Selenium-stabilized carbanions and synthetic studies on the marinopyrroles Open Access

Descriptions

Other title
Subject/Keyword
selenium
carbanions
marinopyrrole
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Fernandopulle, Shimal Chamikara
Supervisor and department
Clive, D.L.J. (Chemistry)
Examining committee member and department
Schieber, A. (Agricultural, Food and Nutritional Sciences)
Clive, D.L.J. (Chemistry)
Cairo, C. (Chemistry)
Vederas, J.C. (Chemistry)
Thompson, A. (Department of Chemistry, Dalhousie University)
Li, L. (Chemistry)
Department
Department of Chemistry
Specialization

Date accepted
2012-05-30T15:02:47Z
Graduation date
2012-11
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
The first chapter of this thesis describes the development of a general route for the generation of selenium stabilized carbanions via a method that bypasses acid catalyzed formation of selenoacetals. Aldehydes are first converted into α-hydroxystannanes by nucleophilic addition of Bu3SnLi. The resulting hydroxyl is then converted to the corresponding phenyl selenide by treatment with PhSeCN and Bu3P to give the α-(phenylseleno)stannane. Upon treatment with BuLi, the α-(phenylseleno)stannane undergoes preferential Sn/Li exchange to give a selenium stabilized carbanion. This carbanion is condensed with an aldehyde to give a β-hydroxy selenide, which can be converted into an allylic alcohol upon oxidation and selenoxide fragmentation. The formation of α-(phenylseleno)stannanes has been applied to aldehydes containing straight and branched alkyl chains, aromatic substituents, and acid sensitive functional groups. The selenium stabilized carbanions have been condensed with aldehydes containing straight and branched alkyl chains, aromatic substituents, and α,β-unsaturation. The second chapter describes synthetic studies towards two marine natural products, marinopyrrole A and B. The synthesis began with the preparation of the unprecedented N,C2 linked bispyrrole core through a Paal-Knorr condensation onto the amino group of ethyl 3-aminopyrrole-2-carboxylate. Preparation of the densely halogenated core of the marinopyrroles through selective chlorination of the bispyrrole seems to be impossible and was not pursued. Due to unexpected alterations to the electronic structure of the pyrrole ring in the presence of electron withdrawing substituents, preparation of a fully functionalized top ring was unsuccessful. Blocking the 3' position of the bispyrrole with a removable blocking group was also unsuccessful by an ortho metallation approach. Preparation of the halogenated bispyrrole starting with the fully functionalized bottom pyrrole seems promising after a model intramolecular conjugate displacement reaction had shown that it is possible to mount the precursor to the top pyrrole on top of the bottom pyrrole. Work is in progress to prepare the mountable precursor to the top ring.
Language
English
DOI
doi:10.7939/R3494Q
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.
Citation for previous publication
Fernandopulle, S. C.; Clive, D. L. J.; Yu, M. J. Org. Chem. 2008, 73, 6018.

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