This thesis describes an investigation into the asymmetric induction found in the electrocyclisation of diazo-componds having α, β, γ, δ-unsaturation. It is thought that the reaction involves two steps, first, an 8 π electron 1,7-electrocyclisation in which orbital overlap at the termini of the π system is achieved <i>via</i> a helical transition state; and second, an intramolecular suprafacial sigmatropic [1,5] hydrogen shift. The results reported here are concerned with the effect of the presence of a chiral substituent at the terminal <i>trans</i> position of the conjugated system in the first step. The second step transfers the chirality stereospecifically, creating a new chiral centre. By measurement of the diastereomeric ratio and a determination of the relative configuration of the two chiral centres, the face selectivity of the chosen chiral groups were assessed. When the medium sized group in the chiral substituent was an alkoxy or hydroxy group, cyclisation at the <i>more</i> hindered face of the alkene in its lowest energy conformation predominated. Polar repulsion effects are thought to be the factors controlling the conformation of the chiral group. When the medium sized group was an alkyl group or an alkoxide ion, the <i>less</i> hindered face was preferred. In the former, steric repulsion effects are believed to dominate the conformation. While, in the latter, polar attraction between the cation and the nitrogen of the diazo-group may stabilize the preferred conformation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:652094 |
| Date | January 1990 |
| Creators | Harding, Mervyn |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/10933 |
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