Synthesis Of Aromatic Ketones And Pyridines By Homogeneous/Heterogeneous Catalysis Of Carbopalladation Of Nitriles

Aryl ketones and pyridine structures are widely present in many pharmaceutical and fine industrial products.In recent decades,carbopalladation of nitrile provides a new idea for the synthesis of aromatic ketones and pyridine.Because the palladium-catalyzed carbopalladation of nitrile is expensive and the catalyst is difficult to recover,so the heterogeneous palladium-catalyzed carbopalladation of nitrile to synthesize aromatic ketones and pyridines has high research value.1.3 wt%Pd/γ-Al₂O₃ heterogeneous catalyst was prepared by impregnation-reduction method to realize the carbopalladation of organobboron compound with aliphatic nitrile.Acetonitrile is involved in the reaction as a solvent and substrate,6-methyl-2,2’-bipyridine was used as ligand and water as additive,the target product was obtained with 92%,at 120℃for 48 hours.It is found that the electron effect has a great influence on the reaction,and the organobboron compound with electron donor substituents can carry out the reaction with good yield;This reaction does not occur with the electron pulling group;Organobboron compound with halogen groups do not work well;The effect of organobboron compound with high steric resistance is also not ideal.The catalyst recovery experiment and characterization,the results show that:The yield of 3 wt%Pd/γ-Al₂O₃ decreased to 37%after five cycles;TEM test showed that the particle size of Pd NPs became larger and gather after the catalyst was used.The results of ICP-MS showed that palladium leaching was large before and after the solution reaction.XPS test showed that the valence state of a small part of Pd changed before and after the reaction.The catalyst was deactivated during the cycle.However,this method still provides a mild and economical strategy for the efficient synthesis of ketones.2.A new[3+2+1]method has been developed for the efficient construction of pyridine framework by the cascade carbon palladium/cyclization reaction of acetonitrile,arylboric acid and aldehyde.Palladium acetate was used as catalyst,1-fluoro-2,4,6-trimethylpyridine-1-trifluoromethanesulfonate as the oxidizer,6-methyl-2,2’-bipyridine was used as the ligand obtain the target product with excellent yield at 95℃for48 hours.The reaction showed good functional group tolerance and substrate universality.It is found that the spatial effect has no effect on aldehydes,and both the electron-giving and electron-pulling substituent groups can react;The reaction can occur with phenylboric acid with electron-giving groups,but not with electron-pulling groups.Steric hindrance effect also has a great influence on the reaction of phenylboric acid.Heterogeneous catalyst 3 wt%Pd/γ-Al₂O₃ has similar catalytic effect to homogeneous catalyst and is also suitable for this reaction.Under the catalysis of heterogeneous catalyst,the system can carry out five rounds of recovery experiments and still maintain high activity.This new method can obtain pyridine and substituted pyridine with very high yield,which opens a new way for the construction of pyridine skeleton by green homogeneous/heterogeneous catalysis method.