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Title: The development of a catalytic asymmetric bromination reaction of alkenes
Author: Redmond, Joanna
ISNI:       0000 0001 3510 879X
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2008
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This thesis describes our investigations into the development of a general method for the catalytic, asymmetric bromination of alkenes. The bromination catalysts employed in the research are ortho-substituted iodobenzenes, which are hypothesised to deliver Br+ to the alkene substrate via a hypervalent I(III)-Br bond. Initially, endeavours to achieve a large scale preparation of our asymmetric bromination catalyst, 2,6-di-[(4R,5R)-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl]iodobenzene, or R-IBAM, are detailed. In order to facilitate this, a large quantity of enantiopure 1,2-diphenylethylene diamine was required to form the chiral amidine moieties of our R-IBAM catalyst. Thus, the development of two novel methods for the synthesis and resolution of 1,2-diphenylethylene diamine are described and the subsequent application of each route to a large scale preparation of the enantiopure diamine. The subsequent novel and optimised preparation of our catalyst to produce 25 g of R-IBAM is detailed. The following studies into the catalytic asymmetric bromination of alkenes include the screening of the various reaction conditions, stoichiometric addition of N-bromosuccinimide to the catalysts and the synthesis and screening of a range of R-IBAM derivatives and analogues. An improved understanding of the catalytic cycle and the possible mechanisms of loss of enantioexcess in our brominated product is detailed. The final section of the thesis describes research into the exchange of Br+ between enantiopure bromonium ions and alkenes. The generation of an enantiopure bromonium ion in the absence of alkene was achieved via the rearrangement of enantiopure bromohydrin, (2S)-1-bromo-1-phenylpropan-2-ol. The intermediate bromonium ion was trapped by chloride to produce the enantiopure bromochlorinated product. This, to the best of our knowledge, represents the first example of the generation and trapping of an enantiopure bromonium ion. Our subsequent investigations into Br+ transfer from the bromonium ion to added alkene are described.
Supervisor: Braddock, Chris Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available