Asymmetric hydrogenation of enamide esters in aqueous media.
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The purpose of this research was to investigate the feasibility of using aqueous media for the synthesis of amino acid precursors through asymmetric hydrogenation reactions. Acetyl-protected enamide esters with a variety of R groups were used in enantioselective hydrogenation reactions to show both the generality of the method and the use of a protecting group that can be easily removed after synthesis. Methyl-2-acetylamino-3-napthyl-2-propenoate and methyl-2-acetylamino-3-phenyl-2-propenoate were synthesized and subsequently hydrogenated in water at 60 psi. These reactions formed protected - amino acid esters methyl-2-acetylamino-3-napthyl-2-propanoate (52.3% yield, 98% ee) and methyl-2-acetylamino-3-phenyl-2-propanoate (92.5 yield, >99% ee) respectively. These results confirmed that water could be used as the solvent for asymmetric hydrogenations of enamide ester materials to synthesize protected - amino acids.
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