NH-Isoxazolidines as Organocatalysts
Doyle, Linda S. (2009) NH-Isoxazolidines as Organocatalysts. PhD thesis, National University of Ireland Maynooth.
This thesis describes the preparation and use of a range of N-unsubstituted bicyclic isoxazolidines as potential organocatalysts in iminium ion and enamine catalysis. The first chapter gives an overview of state-of-the-art organocatalysis. Reactions are discussed in terms of the catalytic mechanism and a selection of reactions catalysed by each route is included. The second chapter discusses the design of two generations of N-unsubstituted isoxazolidine frameworks as potential organocatalysts. The 1st generation, containing a spirocyclohexane adjacent to the secondary amine of an isoxazolidine ring proved difficult to prepare and debenzylation of the parent was problematic. The 2nd generation, based on an isoxazolidine ring fused to a second heterocycle, were successfully prepared and characterised by a combination of NMR spectroscopy, LC/TOF-MS, microanalytical data and x-ray crystallography where necessary. In the third chapter the application of NH-isoxazolidines as catalysts in the Diels-Alder cycloaddition reaction, the Michael addition reaction and the Aldol condensation reaction is discussed. It has been demonstrated that the NH-isoxazolidines are effective in iminium ion catalysis and act as enantioselective organocatalysts for Diels-Alder reactions. The aldol reaction between acetone and p-nitrobenzaldehyde could not be promoted by the NH-isoxazolidines prepared in this thesis. Neither could these catalysts promote the Michael addition reaction with trans--nitrostyrene and a minor amount of the Michael addition product was observed with 1,1-bis(benzenesulfonyl)ethylene as the acceptor. The fourth chapter details the experimental procedures and full characterisation of all new compounds described in this thesis. The appendix carries details of the structures solved by x-ray crystallographic analysis and as a representative a case full description of structural determination of a bicyclic isoxazolidine is detailed. Finally, a complete bibliography of articles referred to in this thesis is included.
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