Highly efficient and enantioselective hydrogenation of quinolines and pyridines with Ir-Difluorphos catalyst

The combination of the readily available chiral bisphosphine ligand Difluorphos with [Ir(COD)Cl]₂ in THF resulted in a highly efficient catalyst system for asymmetric hydrogenation of quinolines at quite low catalyst loadings (0.05-0.002 mol%), affording the corresponding products with high enantioselectivities (up to 96%), excellent catalytic activities (TOF up to 3510 h^-1) and productivities (TON up to 43000). The same catalyst was also successfully applied to the asymmetric hydrogenation of trisubstituted pyridines with nearly quantitative yields and up to 98% ee. In these two reactions, the addition of I₂ additive is indispensable; but the amount of I₂ has a different effect on catalytic performance.