Iridium‐Catalyzed Asymmetric Hydrogenation of Unsaturated Piperazin‐2‐ones

Two different iridium catalyst systems, generated from the ruthenocene‐based phosphine‐oxazoline ligand tBu‐mono‐RuPHOX or the diphosphine ligand BINAP, were developed for the asymmetric hydrogenation of 5,6‐dihydropyrazin‐2(1H)‐ones, affording chiral piperazin‐2‐ones in good yields and with moderate to good ees. Different catalytic behaviors for the hydrogenation of these types of substrate were observed with these two catalyst systems. Our tBu‐mono‐RuPHOX ligand, which bears a ruthenocene scaffold with planar chirality, was found to be the best ligand for the [Ir(L)(COD)]BArF catalyst system, affording the desired products with up to 94% ee. magnified image