Novel rhodium carboxylates as powerful enantioselective catalysts

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Buckley, Aoife
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University College Cork
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This thesis describes the design and synthesis of novel rhodium carboxylates for use as enantioselective catalysts in transformations of α-diazocarbonyl compounds. Enantioselectivities of up to 93% ee were achieved in a C–H insertion reaction leading to a trans 2,3-dihydrobenzofuran, which is the highest enantiopurity reported for this compound to date. Chapter one focuses on the literature background of intramolecular C(sp3 )–H insertion reactions, specifically how catalyst and substrate effects may influence the chemo-, regio- and stereoselectivity of α-diazocarbonyl transformations, thus providing context for this work. Chapter two describes the design and synthesis of the rhodium carboxylate complexes. The catalysts were inspired by the rhodium mandelate skeleton but were adapted to incorporate a menthyl or fenchyl chiral auxiliary in addition to variation of the aromatic moiety. Formation of the novel rhodium carboxylates led to an unanticipated observation and the impact of the relative stereochemistry on the mechanical properties of crystals was investigated. Chapter three outlines the application of the novel rhodium carboxylates in a series of carbenoid mediated transformations including C–H insertion, oxonium ylide formation-[2,3]-sigmatropic rearrangement, aromatic addition and cyclopropanation. The highest enantioselectivities were obtained in C–H insertion to afford the trans 2,3- dihydrobenzofuran moiety in up to 93% ee and in oxonium ylide formation-[2,3]- sigmatropic rearrangement 74% ee. Chapter four describes the synthesis of chiral bisoxazoline ligands and their application in copper-bisoxazoline catalysed C–H insertion reactions of αdiazocarbonyl compounds. Chapter five contains the experimental details and spectral characterisation of all compounds synthesised in this project, while details of chiral stationary phase HPLC analysis and X-ray crystallography are included in the appendices.
Bisoxazoline , C-H Insertion , Rhodium carboxylates , Enantioselective catalysts
Buckley, A. 2019. Novel rhodium carboxylates as powerful enantioselective catalysts. PhD Thesis, University College Cork.