Phenazine Radical Cations as Efficient Homogeneous and Heterogeneous Catalysts for the Cross‐Dehydrogenative Aza‐<i>Henry</i> Reaction
Felix Unglaube, Paul Hünemörder, Xuewen Guo, Zixu Chen, Dengxu Wang, Esteban Mejía
Abstract
Abstract The redox activity of molecular phenazine catalysts has been previously exploited for aerobic oxidative amine homo‐ and cross‐coupling reactions. In this contribution, we have extended the reaction scope of this novel type of organocatalyst and used them in the cross‐dehydrogenative aza‐ Henry coupling of isoquinolines with nitromethane under aerobic conditions. Additionally, we have designed and prepared a novel porous organic polymer by cross‐linking of tetrakis(4‐bromophenyl)silane and dihydrophenazine through Pd‐catalyzed Buchwald‐Hartwig cross‐coupling. This new type of heterogeneous catalyst, apart from being robust and easily reusable, also showed outstanding catalytic activities and improved selectivity compared to its molecular counterpart. A plausible reaction mechanism was proposed based on spectroscopic and kinetic measurements.