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Title: Asymmetric syntheses involving keto-esters
Author: Bovey, Doreen M.
Awarding Body: University of London
Current Institution: Royal Holloway, University of London
Date of Award: 1950
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The partial asymmetric syntheses performed by McKenzie involving Grignard reactions on optically active alpha-keto-esters. [diagram] are discussed, and a mechanism for the course of such syntheses is proposed. The reaction is probably influenced primarily by asymmetry in the electromagnetic field in the neighbourhood of the alpha-carbonyl group, induced by the asymmetric field in the optically active centre, and also by the differing free energies of intermediate diastereoisomeric Grignard complexes formed during the reaction. The resultant asymmetric synthesis is therefore directed by a combination of these effects, and not by any single force of "asymmetric induction" as originally postulated by McKenzie. This hypothesis is substantiated by reference to the two complementary syntheses of [diagrams] as the sign of rotation of the product and the degree of asymmetric synthesis are shown to depend on both the above factors. The effect of increasing the separation between the asymmetric and reaction centres in such syntheses has been studied by performing Grignard reactions on the homologous series of (-)-menthyl ketoesters, [diagram] Asymmetric synthesis takes place when n = 2 or 3, and the relationship between the hydroxy-acids and their corresponding lactones formed in these reactions has been investigated. Laevorotatory acids, giving dextrorotatory lactones of higher specific rotation than the parent compound were obtained, the degree of asymmetric synthesis being only slightly dependent on the conditions of reaction. No optical activity could be detected in the hydroxy-acids formed when n= 4 or 8, probably because the electromagnetic induction effect is dissipated along the methylene chain, and the difference in free energy between the diastereoisomeric Grignard complexes is too small to effect any observable asymmetric synthesis.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Organic Chemistry