Chemo- and Enantioselective Hydrogenation of α-Formyl Enamides: An Efficient Access to Chiral α-Amido Aldehydes

In order to effectively synthesize chiral alpha-amino aldehydes, which have a wide range of potential applications in organic synthesis and medicinal chemistry, a highly chemo- and enantioselective hydrogenation of alpha-formyl enamides has been developed, catalyzed by a rhodium complex of a P-stereogenic bisphosphine ligand. Under different hydrogen pressures, the chiral alpha-amido aldehydes and beta-amido alcohols were obtained in high yields (97-99 %) and with excellent chemo- and enantioselectivities (up to >99.9 % ee). The hydrogenation can be carried out on a gram scale and with a high substrate/catalyst ratio (up to 20 000 S/C), and the hydrogenated products were further converted into several important chiral products. Computations of the catalytic cycle gave a clear description for the R/S pathways, provided a reasonable explanation for the enantioselectivity, and revealed several other specific features.