Hydrogens Ethyl 3-Hydroxybutanoate

In ethyl 3-keto-2-oximino-3-phenylpropanoate catalytic hydrogenation over palladium on carbon reduced both the keto and oximino group, giving a 74% yield of ethyl ester of -phenylserine (ethyl 2-amino-3-hydroxy-3-phenylpropionate). The reduction is stereospecific and only the erythro dia-stereomer was obtained, probably via a cyclic intermediate 11097]. Similarly, hydrogenation over Raney nickel at 25-30° and 1-3 atm converted ethyl a-oximimoacetoacetate quantitatively to ethyl 2-amino-3-hydroxybutanoate [45]. 

The enantioselective hydrogenation of methyl or ethyl 3-oxobutanoate to give methyl or ethyl 3-hydroxybutanoate is a model reaction for the preparation of 3-hydroxyalkanoic acids, ail important class of compounds which comprise key intermediates in the synthesis of natural products and in the biosynthesis and metabolism of fatty acids. 

The alkyl esters of 3-hydroxybutanoic acid are a particularly useful group of compounds in organic synthesis because they are available in both chiral forms. Ethyl (5)-3-hydroxybutanoate, for example, may be prepared by the reduction of ethyl acetoacetate on the re side of the keto group with fermenting yeast and leads to an enantiomeric purity of about 85% which may be enriched further via a crystalline dinitrobenzoate. Synthesis of the R form was a little more difficult but could be achieved with 83-88% purity by the reduction of the acetoacetate with hydrogen in the presence of Raney nickel which had been treated with tartaric acid. " ... 

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