Asymmetric hydrogenation of enamide esters in aqueous media.

Abstract

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.