Polymer-Supported Electron-Rich Oxime Palladacycle as an Efficient Heterogeneous Catalyst for the Suzuki Coupling Reaction

Various electron-rich oxime palladacycle resins designed as heterogeneous catalysts were employed for the Suzuki coupling reaction of aryl halides with arylboronic acids. The electron-richness of the oxime ligand was controlled by the substituted alkoxy groups. Evaluation based on the electronic effect of the catalysts revealed that the alkoxy-substituted oxime palladacycle resins showed better catalytic activity than palladated Kaiser oxime resin in the Suzuki coupling reactions and that the catalytic activity of oxime palladacycle resins increased as the electron-richness of oxime ligand increased. The most electron-rich oxime palladacycle resin exhibited an excellent catalytic performance for the synthesis of both biaryl and heterobiaryl compounds, despite its heterogeneous system. As a practical application of the catalyst, a valsartan precursor was synthesized in high yield under mild conditions. The electron-rich oxime resin could also be reused for up to 5 cycles while maintaining good catalytic activity in the Suzuki coupling reaction.