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Recoverable ligands for the Sharpless Asymmetric Epoxidation

Morgan, Ian Rhys. 2005. Recoverable ligands for the Sharpless Asymmetric Epoxidation. PhD Thesis, Cardiff University.

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The aim of this work was to synthesise a polymer supported ligand for the Sharpless Asymmetric Epoxidation, which could be recovered with ease and then reused without significant reduction in the enantiomeric excess in the epoxy-alcohol product. A 6/s-dihydroxy ester model system was synthesised that featured the removal of the "redundant esters" as present in the tartrate system and successful epoxidations led to this system being incorporated into a polymer supported ligand. A polymer supported system was synthesised but the showed low selectivity in asymmetric epoxidations. The model system was further investigated and it yielded highly selective ligands for the Sharpless Asymmetric epoxidations and in optimal cases was directly comparable to the Sharpless tartrate system. After practical obstacles had been overcome, a ligand was formulated that could be recovered post-epoxidation in good yield by relatively simple solvent manipulations. This recovered ligand could then be re-used without significant loss in enantioselectivity and represented the synthesis of a recoverable ligand for the Sharpless asymmetric epoxidation, a leader in the field. The ligand was further tested in the kinetic resolutions of secondary allylic alcohols and this novel ligand system equalled the tartrate system and in optimal cases the enantiomeric excess of the secondary allylic alcohols were higher than the tartrate system. Serendipitously, the most tested ligand in the asymmetric epoxidations performed the phenomena of gelation, the spontaneous self organisation of the ligand/gelator solution, forming a supramolecular molecular structure that exhibited no flow, a gel. Derivatives of this "gelator" were synthesised in the search for further examples and in order to determine the origin of this phenomenon. Further gelators were discovered and these all contained a distinct functional similarity to the original discovery and these gelators were capable of gelling a wide range of solvents. The apparent gel-forming functionality was incorporated into a bis-acetylene moiety in an attempt to create a conducting material and this bis-acetylene was subsequently polymerised to form a coloured gel containing the poly(eneyne) moiety.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
ISBN: 9781303205194
Date of First Compliant Deposit: 30 March 2016
Last Modified: 12 Feb 2016 23:15

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