Designing new chiral hydroxamic acid ligands for the asymmetric epoxidation reaction in water.
PhD thesis, University of Glasgow.
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Herein, we report the synthesis of new chiral hydroxamic acid ligands for the V-catalysed asymmetric epoxidation reaction in aqueous solution.
During the course of this project, a wide range of allylic alcohols were epoxidised under mild reaction conditions. The target epoxides were isolated in good-to-excellent yields with up to 94% ee.
To further develop the project, we also report that the range of substrates has been extended to unfunctionalised alkenes. These materials have been successfully converted to the corresponding allylic alcohols in the presence of SeO2 and acetic acid. Asymmetric epoxidation was then achieved under anhydrous conditions in good-to-moderate yields with up to 76% ee and in certain cases, the overall transformation can occur as a one-pot process.
A brief investigation into the development of organocatalytic transfer hydrogenation mediated by chiral pyridines has also been carried out. In this project, a range of chiral quarternary ammonium salts have been prepared as precursors to the corresponding dihydropyridines.
It was our initial intention to utilise these chiral dihydropyridines in the enantioselective reduction of imines. This would result in the formation of the desired chiral amine and a quaternary pyridinium salt, which could then be reduced to reform the dihydropyridine in a catalytic cycle.
However, with all pyridinium salts formed we were unable to produce the target dihydropyridines and this project was consequently abandoned.
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