Design and use of novel metal catalysts in organic synthesis

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Fitzgerald, Deirbhile
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University College Cork
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This project focuses on the design and synthesis of novel dirhodium carboxylate catalysts, and their precursor ligands, for use as enantioselective catalysts in transformations of α-diazocarbonyl compounds. Chapter One focuses on the literature background over the past thirty years in transition metal-catalysed asymmetric transformations of α-diazocarbonyl compounds. This overview aims to give an insight into the use of both copper and rhodium-based catalysts in intramolecular and intermolecular C-H insertion reactions, cyclopropanation and desymmetrisation reactions. The evolution of dirhodium carboxylate design since the 1980s is explored. This summary provides insight into their use as enantioselective catalysts in asymmetric transformations of α-diazocarbonyl compounds, thus providing context for this work. Chapter Two describes the design and synthesis of novel, enantiopure dirhodium carboxylate complexes, drawing inspiration from the rhodium (S)-mandelate skeleton. Initially, two enantiopure rhodium carboxylates were synthesised, incorporating carboxylic acid ligands bearing a fenchyl chiral auxiliary. Synthesis of carboxylic acid ligands bearing a bulky adamantyloxy group or a tert-butoxy group in place of the fenchyl substituent was investigated to simplify the stereochemical features, with just one stereogenic centre in each ligand. Two target carboxylic acids were obtained in racemic form, one bearing an adamantyloxy group and the other bearing a tert-butoxy group adjacent to the carboxylic acid moiety. Resolution of these carboxylic acids was explored through formation of diastereomeric salts or enzymatic kinetic resolution; while enantioenrichment was observed, further work is required to obtain the ligands in an enantiopure form for catalyst preparation. Chapter Three describes the synthesis of both racemic mandelamide and enantiopure (S)-mandelamide. In addition, a pair of diastereomerically pure mandelamides with α-methylbenzylamine were synthesised and characterised. The mandelamides were prepared to enable exploration of their crystal landscape in collaboration with another research group in UCC. Chapter Four contains the full experimental details and spectroscopic and analytical characterisation of all compounds synthesised in this project, while details of chiral stationary phase HPLC analysis are included in Appendix 1.
Rhodium catalysis
Fitzgerald, D. 2023. Design and use of novel metal catalysts in organic synthesis. MRes Thesis, University College Cork.
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