Enantioselective Access to Chiral Vicinal Diamines via Rhodium-Catalyzed Consecutive Reductive Amination/Asymmetric Transfer Hydrogenation of Quinoline-2-carbaldehydes with Anilines

Rhodium-catalyzed one-pot tandem reductive amination/asymmetric transfer hydrogenation of quinoline-2-carbaldehydes with anilines using HCO₂H/NEt₃ reductant has been developed for enantioselective synthesis of chiral <i>N</i>,<i>N</i>'-diaryl vicinal diamines. The reaction tolerates various anilines and quinoline-2-carbaldehydes, affording chiral <i>N</i>,<i>N</i>'-diaryl vicinal diamines in high yields with excellent enantioselectivities (up to 99% ee). The enantiocontrol is achieved by the judicious selection of transition-metal catalyst, reductant, and additive. The observed enantioselectivity can be rationalized by analyzing the critical interactions within the key transition state structure.