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Title: Novel Ketone Catalysts for Asymmetric Epoxidation of Alkenes
Author: Bettati , Michela
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2008
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Chiral non-racemic ketones have been shown to be powerful promoters of asymmetric induction in epoxidation reactions with alkenes in the presence of Oxone®. However, the catalyst structural features are specific for the class of olefins used as substrates. Up to date, excellent results have been achieved for trans- and trisubstituted alkenes, while terminal alkenes still represent one of the most challenging areas. Much work needs to be done in developing suitable catalysts to lead to high enantioselectivities. Previous work in Armstrong’s group identified ketone catalysts based on oxabicyclo[3.2.1]octan-3-ones and on the N-carboethoxytropinone skeleton, which performed very well in enantioselective epoxidation of trans- substituted olefins (up to 93% ee for E-stilbene). This thesis describes the synthesis and the efficiency towards alkene epoxidations of novel a,a-disubstituted ketones based on the Ncarboethoxytropinone scaffold. In particular, encouraged by the positive results achieved by Shi’s group for terminal alkenes, several spiro-motifs a to the carbonyl have been investigated. A slight improvement was observed towards the challenging terminal olefins compared to the monosubstituted ketone analogues, whilst very high ee were maintained for trans- substituted alkenes. However, to our surprise, only minor changes in enantioselectivity were observed from modifications of the steric and electronic properties of this spiro-motif in the ketone catalyst. Further axial or equatorial a functionalisation was explored as a possible strategy to increase enantioselectivity towards terminal and 1,1-disubstituted alkenes. Indeed, significant improvements were achieved in enantioselective epoxidation of styrene (up to 50% ee) and a-methyl styrene (up to 39% ee).
Supervisor: Armstrong, Alan Sponsor: Merck ; GSK Verona
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral