High Circulating Palladium (0) Diphenyl Catalyzed Coupling Reaction

Many natural products containing the unit of biaryls are the importantconstitutional units of pharmaceuticals and functional materials. Suzuki couplingreaction is widely applied as a powerful tool to synthesize biaryls due to its highefficiency, low cost and mild condition. In this paper, three new systems of the Pd (0)–catalyzed Suzuki reaction and Suzuki-type self–coupling reaction were developed.First of all, the new system of18–Crown–6promoting Suzuki reaction catalyzedby Pd/C was developed. The reaction conditions including18–Crown–6, temperature,base, solvent and atmosphere were investigated carefully. The optimized processconditions were developed. Thirty–three compounds of biaryls were successfullysynthesized by this process.Secondly, an efficient and recyclable protocol to the Suzuki reaction catalyzed byPd/PVP was developed. When the polyvinyl pyrrolidone (PVP) was used as astabilizing agent, the palladium nanoparticles were successfully synthesized. In thepresence of Pd/PVP, the cross-coupling reaction of aryl halides and arylboronic acidproceed smoothly in PEG-400as a green solvent. The optimized reaction conditionswere reached after investigating the influence of temperature, base, solvent andatmosphere. Twenty compounds of biaryls were successfully synthesized using this newsystem. Furthermore, the system of Pd/PVP can be recycled at least five times withoutloss of catalytic activity.Finally, the catalytic system for self-coupling of arylboronic acid was successfullydeveloped. Under the optimized conditions (2.0mol%Pd/C, H2O, NaOH,80℃in air),the self-coupling of arylboronic acid could be completed fast and afford good yields.The method is eaily operated and environmentally friendly. More over, the ligand andoxygenant were not necessary to add in the reaction.