The Stereochemistry of Nucleophilic Addition. I. The Reformatsky Reaction of 2-Methyl- and 2-Ethylcyclohexanones

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The Reformatsky reaction of 2-methyl- or 2-ethylcyclohexanone with ethyl bromoacetate gave a mixture of epimeric alcohols, which were then separated by column chromatography in an 80 : 20 ratio. The configurations of these major and minor products were identified as ethyl <I>trans</I>- and ethyl <I>cis</I>-2-methyl (or ethyl)-1-hydroxycyclohexylacetate respectively on the basis of their IR analyses, their chromatographic behavior, and correlation with the products of the Grignard reaction, the stereochemistry of which is well known. The NMR spectra of these epimeric alcohols are also discussed, and it is suggested that the chemical shifts of the methylene protons alpha to the ethoxycarbonyl group and of the proton of the hydroxyl group gives useful data for their stereochemical assignments. From these results, it is evident that the Reformatsky and the Grignard reactions proceed in a similar fashion; that is, the entering group predominantly approaches to the carbonyl group from the equatorial side. The stereoselectivity of the Reformatsky reaction is slightly less than that of the Grignard reaction.
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