Iridium‐Catalyzed Hydrogenation of β‐Dehydroamino Acid Derivatives Using Monodentate Phosphoramidites

The iridium‐catalyzed asymmetric hydrogenation of 13 different β‐dehydroamino acid derivatives to give optically active β‐amino acid esters has been examined. Readily accessible monodentate octahydrobinaphthol‐based phosphoramidites were used as chiral ligands. Good to excellent enantioselectivities and yields were obtained for the E isomers, whereas poorer catalyst performance was found for the Z isomers. Importantly, to obtain high enantioselectivity, substitution at the 3,3′‐positions of the ligands was necessary. Enantioselectivities of up to 94 % ee were achieved under optimized conditions.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)