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Title: Nickel catalysis of asymmetric conjugate addition reactions
Author: Sian, Sudipinder K.
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 1999
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The potential for inducing chirality upon 1,4-conjugate addition to alpha/beta unsaturated carbonyls has captivated the interest of many chemists for over 20 years. Metals such as copper, cobalt and nickel have been used as the catalytically active metal centres in these enantioselective reactions. The work presented in this thesis describes the development of a new nickel catalysed system, the attempts at employing it on a range of substrates and ultimately making the chemistry stereoselective. The Introduction reviews metal-mediated syntheses popularly used in organic reactions. Emphasis is put on the development of the conjugate addition reaction. The use of various organocopper reagents, either in stoichiometric or catalytic amounts, in these reactions is described. The impact of organozinc reagents in this field of chemistry is discussed, and its application in the recent, successful advances in this area. In order to investigate the scope of nickel catalysed reactions, initial studies covered the extent of the applicability of the catalyst on a range of substrates, both from commercial sources and some prepared in-house. The Results and Discussion describes the attempts at inducing enantioselectivity. Due to limitations in the compatibility between the catalyst and the chiral ligands, a new pre-catalyst, nickel tert-butoxide, was prepared. Preliminary results of using this catalyst for the first time in conjugate addition reactions are documented. One example of a reduction of an allylic acetate has also been discovered. Attempts at reduction on other allylic acetates were undertaken. The endeavours at designing a new, chiral catalytic system with this catalyst are discussed, with the emphasis on employing hydroxyphosphine ligands. Difficulties in controlling the oxidation state of phosphine in their syntheses preceded the screening of a number of ligands with the catalyst. Although low enantioselectivities were recorded, in some cases, there was acceleration in rates of reaction and the catalyst was found to tolerate a range of ligands possessing a variety of functionalities. In, summary, a new nickel(II) catalyst has been identified which may be active in carbon-hydrogen and a number of carbon-carbon bond forming reactions. Finally, the Experimental section is a collection of experiments and related data carried out during the project.
Supervisor: Berrisford, David J. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available