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Title: The 1,5- hydride shift as a route into nitro-Mannich cyclisation
Author: Ware, Oliver
ISNI:       0000 0004 7661 2353
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2018
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Carbon-hydrogen bonds are typically not viewed as a reactive site, rather they are commonly the backbone of the molecule to which functional groups are attached. We believed that we could find a method of reacting directly at C-H bonds via a hydride transfer to provide a simple, atom efficient method of constructing carbon-carbon bonds, providing a new target site for small molecule synthesis. Our initial targets for C-H activation were benzylic ethers. This was to be achieved with the use of Lewis acid catalysts to promote hydride transfer. It was initially thought that this transformation could be achieved through a modification of the Oppenauer oxidation, which had previously shown a small degree of conversion (8%) within the group. The yield was improved to 24%, but no further progress was made despite inquiry into a wide range of conditions and substrates. These results led us to consider a method of intramolecular C-H activation which would be achieved via a 1,5-hydride shift. This reaction has seen use previously with electron withdrawn alkenes, but only a very limited number of nitroalkenes had been observed performing this transformation, using a protic solvent. We have developed a method of Lewis acid catalysis to convert nitrostyrene substrates. The nitrostyrene acts as a hydride acceptor to form a nitronate anion, which then attacks the newly generated cation to form a six-membered ring. A novel route into the synthesis of substituted tetrahydroquinolines has been achieved via a nitro-Mannich cyclisation, something only previously performed with n-BuLi mediated deprotonation of nitroalkanes or the use of an external hydride source to generate the required nitronate. Our reaction has the potential to be incredibly atom efficient, with no gain or loss of mass from the starting material to product, requiring only the use of a catalyst.
Supervisor: Anderson, J. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available