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Title: Gas phase rearrangements of 2-pyrones
Author: Cartwright, Gary A.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1992
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The automerisation and decarbonylation processes of 2-oxo-2H-pyran-5-carboxaldehyde have been investigated via Flash Vacuum Pyrolysis (F.V.P.) techniques, using 16O and 2H labelled precursors. The products were analysed by 1H, 2H and 13C nmr spectroscopy and, where necessary, by mass spectrometry. The observed rearrangements can be explained by invoking reversible electrocyclic ring opening of the 2-pyrone system to ketene intermediates with accompanying [1,5]-signatropic shifts and carbon-cation double bond isomerisations. The mechanism of decarboxylation of 2-oxo-2H-pyran-5-carboxylic acids has been investigated and can also be explained by invoking ring opened intermediates. It was found that a methyl group at C-6 of the 2-pyrone system has two major influences; firstly it blocks the sigmatropic shift process and hence hinders the decarbonylation of the 2-oxo-2H-pyran-5-carboxaldehydes. The temperature dependence of the ring opening process has been invstigated by changing the ring oxygen hetero atom of the 2-pyrone system to nitrogen. This pyridone system has been examined using 15N labelled compounds, the ring opening of which was found to occur at much higher furnace temperatures. A convenient pyrolytic method of making various substituted coumarins from easily synthesised acrylate compounds has also been discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available