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Exploring iminium ion catalysis

Gibbs, Timothy John 2008. Exploring iminium ion catalysis. PhD Thesis, Cardiff University.

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Abstract

This thesis is composed of two central themes of research Chapters 2-6 describe efforts to understand and increase the activity of iminium ion catalysts. Chapters 7-9 are free-standing investigations exploring concepts and observations that were encountered through the course of the research. Chapter 1 briefly introduces iminium ion catalysis before discussing the experimental and theoretical techniques that are routinely applied to investigate reaction mechanism. The discussion of techniques is divided into three sections structural, kinetic and theoretical methods. This is followed by a passage that highlights the reported techniques that have been applied to understand mechanisms of iminium ion catalysed processes. Chapter 2 highlights the work previously conducted within the group developing catalysts for the iminium ion catalysed Diels-Alder reaction and describes a SAR study designed to understand the relationship between the cc-effect and P-EWG components of catalysts to aid future catalyst design. The study found that the components work independently. Chapter 3 describes a further SAR study conducted to provide evidence for the role of the P-EWG in increasing catalyst activity. The important conclusions drawn were that P-EWG was not acting as a proton shuttle as previously hypothesised and that EWG's that do not contain a carbonyl group could be exploited to increase the activity of a catalyst. Chapter 4 describes investigations into mechanistic aspects of the catalytic cycle for the iminium ion catalysed Diels-Alder reaction. The isolation of key iminium ion intermediate allowed for structural studies and kinetic investigations of the individual steps of the catalytic cycle. The Diels-Alder cycloaddition was found to be the RDS and the physical reasons for this were understood. The hypothesis was formed that a lowering in the LUMO energy of the dienophile by including a strong p-EWG into the catalyst would accelerate the overall catalytic cycle. Chapter 5 describes the application of our findings to the design and synthesis of more active catalysts based around the scaffold of MacMillans imidazolidinone catalyst. The inclusion of an additional p-EWG within the catalyst scaffold provided unprecedented levels of activity supporting our hypothesis. The development and evaluation of a predictive theoretical tool for catalytic activity is also discussed. Chapter 6 shows the preliminary development of piperazinones as catalyst for the iminium ion catalysed Diels-Alder reaction of aldehydes and ketones. Chapter 1 describes our efforts to develop a chiral dynamic resolution procedure for the iminium ion catalysed Michael addition reaction of nitroalkanes to cc,p-unsaturated ketones. Chapter 8 reports the development of a one-pot monocarboxymethylation procedure for primary amines and diamines using glyoxylic acid under mild conditions. Chapter 9 describes the first aminocatalytic method for the preparation of non-natural and natural bis-indolyl alkanes.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
ISBN: 9781303212888
Date of First Compliant Deposit: 30 March 2016
Last Modified: 17 Jun 2017 08:29
URI: http://orca-mwe.cf.ac.uk/id/eprint/54688

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