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Improving synthetic efficiency through C—H activation

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Title: Improving synthetic efficiency through C—H activation
Author(s): Covell, Dustin J.
Director of Research: White, Maria C.
Doctoral Committee Chair(s): White, Maria C.
Doctoral Committee Member(s): Denmark, Scott E.; Hergenrother, Paul J.; Gruebele, Martin H.
Department / Program: Chemistry
Discipline: Chemistry
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: Ph.D.
Genre: Dissertation
Subject(s): C-H Activation Efficiency Palladium
Abstract: Selective C—H activation methods provide a complementary approach for synthesizing complex small molecules, which traditionally are constructed by chemists using C—C bond forming reactions to join preoxidized fragments. Furthermore, the strategic application of C—H activation reactions has considerable potential for improving the overall efficiency of synthetic endeavors by introducing functionality directly into preassembled hydrocarbon frameworks, mitigating the effect of having to carry reactive functionality throughout a reaction sequence. With this goal in mind, this work describes a series of projects that develop and implement novel C—H oxidation reactions and strategies. Firstly, a mild and efficient oxidation strategy for the preparation of chiral polyols is presented and validated through an enantioselective synthesis of differentially protected L-galactose. This synthesis is enabled by the development of a highly regio- and stereoselective linear allylic C—H oxidation reaction that generates 4-methoxybenzoate derivatives of chiral (E)-2-butene-1,4-diols directly from readily available chiral homoallylic alcohols and carboxylic acids. Secondly, this work details the discovery of a heterobimetallic Pd(II)bis-sulfoxide/(Salen)Cr(III)F catalyst system for asymmetric allylic C—H oxidation of terminal olefins. Evidence is provided that supports a model in which a chiral Lewis acid co-catalyst interacts with an organometallic intermediate and influences the stereochemical course of the catalytic process. Additionally, this work establishes that the asymmetric branched allylic oxidation reaction can be combined with other enantioselective transformations to afford enantiopure, polyoxygenated allylic alcohols rapidly and in good yields. Thirdly, this work outlines the development of a novel catalytic palladium(II)-based method for the conversion of ketones, ketoesters, and aldehydes directly to their unsaturated homologs, without the need for prior activation of the carbonyl. Importantly, this reaction shows good to excellent reactivity and unprecedented selectivities for a number of substrates with a diverse array of functional groups. Preliminary mechanistic studies suggest the reaction proceeds through a Pd-enolate intermediate that undergoes successive beta-hydride elimination to give the desired unsaturated carbonyl compounds, and that the acid additive is a key promoter of the reaction.
Issue Date: 2012-02-01
URI: http://hdl.handle.net/2142/29435
Rights Information: Copyright 2011 Dustin J. Covell
Date Available in IDEALS: 2014-02-01
Date Deposited: 2011-12
 

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