UBC Theses and Dissertations
Asymmetric syntheses in the alkylation of substituted acetic esters Rolston, John Henry
An attempt has been made to develop a model for predicting the course of an asymmetric alkylation. Thus, by considering the influence of an asymmetric center upon a reaction center located in an adjoining plane, a preferred conformation of the intermediate anion is selected. This conformation is used to predict the stereochemistry of the product. The model correctly predicts the stereochemical result of several reactions known in the literature. The (-) isobornyl and (-) menthyl esters of 2-methylbutyric acid were alkylated with 1-bromobutane in 42% yield. Both of the alkylated esters were reduced with lithium aluminium hydride and the 2-methyl-2-ethylhexan-1-ol isolated by gas-liquid chromatography was shown to be optically inactive. The lack of an observable rotation does not permit a critical evaluation of the proposed model in these instances. The major impurities present in the alkylation of the aforementioned esters, namely the n-butyl ether of the optically active alcohol, have been identified by independent syntheses.
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