| In 1991,Separation and characterization of nitrogen-heterocyclic carbene(NHC)led to the rapid development of research on nitrogen heterocyclic carbene by Arduengo.Since then,today’s N-heterocyclic carbene has become one of the most powerful tools in organometallic chemistry and systhesis chemistry,and it has a wide range of applications in the industrial field.The paper mainly studied the application of nitrogen heterocyclic carbene ligands in the synthesis of heterocycles such as pyridine ring and furan ring.Using nitrogen heterocarbene ligands for catalyst,the reaction can get to selective synthesis specific rings such as furan,pyrane and other heterocyclic molecules.The heterocycles molecules have biological role in the synthesis of natural drugs.In the past,the Diels-Alder reaction is good way to build the rings,but this requires more rigorous conditions and the reaction is more difficult.However,this research can use an enyne as a substrate and NHC-Ni(0)as a catalyst,it is successfully construct the heterocyclic molecule.The reaction have some advantage such as highly efficient,inexpensive,and mild conditions.NHC is regarded as the extension and development of organic phosphine ligands.Compared with traditional P ligands,NHC ligands have many advantages.(1)Conjugation is strong.(2).strong σ-electron donating ability and weak π-electron accepting ability.(3)The structural transformation is easy.(4)Ligands are readily available and inexpensive.In the process of metal coordination,σ-electron can be provided to the metal.At the same time,the central metal has a feedback effect on the carbene carbon atom,so that the NHC-metal complex can be stable in long time.It has been found that nickel-nitrogen heterocyclic carbene can be used as a catalyst to selectively synthesize specific heterocyclic rings,such as nitrogen-containing or oxygen-containing heterocycles.The research overcomes the side reactions of enyne which is the trimerization reaction of alkynes and the dimerization of the enyne by controlling steric hindrance and electronic effects.The reaction have good yield and the reaction mechanism is explained. |
