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Mechanistic Investigation, Development and Synthetic Applications of a Catalytic Enantioselective and Diastereoselective Allylboration Methodology Open Access

Descriptions

Other title
Subject/Keyword
Asymmetric Catalysis, Allylboration, Allylboronate, Palmerolide A
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Rauniyar, Vivek
Supervisor and department
Dr. Dennis G. Hall (Chemistry)
Examining committee member and department
Frederick G. West, Department of Chemistry, Jeffrey M. Stryker, Department of Chemistry, Steven H. Bergens, Department of Chemistry, Kamaljit Kaur, Faculty of Pharmacy and Pharmaceutical Sciences, William D. Wulff, Department of Chemistry, Michigan State University
Department
Department of Chemistry
Specialization

Date accepted
2009-09-11T15:00:40Z
Graduation date
2009-11
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
Over the past two decades and continuing on, carbonyl allylation chemistry has been a very useful and popular tool for the stereocontrolled formation of carbon-carbon bonds in the field of organic synthesis. In the context of natural product synthesis, the efficiency and status of aldehyde allylboration method is only matched by the asymmetric and diastereoselective aldol methodology. Unfortunately, prior to the new millennium, the means to control the absolute stereoselectivity in the addition of allylic boron reagents had been restricted to stoichiometric chiral directors, appended onto the metal center. In 2002, the research groups of Hall and Miyaura reported a new Lewis acid-catalyzed allylboration reaction manifold, which raised intriguing mechanistic questions and also paved the way for a catalytic enantioselective methodology development. Chapter 2 of this thesis details mechanistic studies related to the new Lewis acid-catalyzed allylboration. In this chapter, various control experiments and kinetic studies are presented, the results of which allowed us to propose a hypothesis involving the electrophilic boronate activation as the key factor for the observed rate enhancement. Chapter 3 describes the initial phase of our research to develop a catalytic enantioselective allylboration methodology. We discovered that Brønsted acid catalysts derived from diol•SnCl4 complexes were promising catalysts for the asymmetric addition of air and moisture stable and commercially available allylic pinacol boronates. Under this 1st generation catalyst-system, the corresponding homoallylic alcohols were obtained in moderate to good enantioselectivity and excellent diastereoselectivity. The development of a novel chiral Brønsted acid catalyst for the highly enantio- and diastereoselective allylboration reaction methodology is the single most important result to come from this thesis. Chapter 4 outlines the development of the 2nd generation catalyst system. A systematic study of the diol component of the catalyst system led us to arrive at a novel diol nicknamed Vivol on behalf of my contribution. The resulting Brønsted acid derived from Vivol•SnCl4 now provided the corresponding homoallylic alcohol products in very good to excellent enantioselectivity. Preliminary mechanistic studies along with the X-ray diffraction structure of the catalyst system are also presented. Based on this information, an even better performaning diol (termed F-Vivol) was developed. This 3rd generation catalyst system derived from F-Vivol•SnCl4 complex was shown to display consistently superior reactivity and selectivity over its 2nd generation predecessor. Chapter 5 describes our efforts to expand the reagent scope of the Brønsted acid catalyzed allylboration methodology. Furthermore, this chapter also describes the successful application of the catalytic process towards the synthesis of simple and complex molecules. Accordingly, the preparation and application of the Brønsted acid-catalyzed addition of 2-bromoallyl boron pinacolate is described. The successful transformation of the corresponding bromo-homoallylic alcohols to a compelling class of γ-butyrolactones is also presented. The later part of the Chapter presents the synthesis of natural products (+) dodoneine and palmerolide A.
Language
English
DOI
doi:10.7939/R32328
Rights
License granted by Vivek Rauniyar (rauniyar@ualberta.ca) on 2009-09-10T17:49:08Z (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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