Copper-Catalyzed Oxidative Of Oxime Esters And Glycine Esters: Synthesis Of Substituted Pyridines

Pyridines and quinoxalines are two kinds of very important nitrogen-containing heterocyclic compounds.The paper focused on different applications and synthetic strategies of pyridine compounds in recent decades.The new methods of copper-catalyzed synthesis of poly-substituted pyridines and the synthesis of quinoxalines were also introduced in this paper.The main body contains the following three parts:Firstly,we mainly made a comprehensive overview of the application and synthetic methods of pyridine compounds.On one hand,the pyridine compounds have a wide range of applications in biochemistry,chemical chemistry,pesticide chemistry,organic synthesis chemistry,functional materials,dyes,and many other fields because of their biological and pharmaceutical activities which due to the existence of pyridine ring structure.On the other hand,according to the synthesis of pyridine compounds with or without metal catalysis and metal-catalyzed synthesis type,we classified and summarized their synthetic methods.We found that metal-free catalytic synthesis methods of pyridine have the advantages of economic,environmental,and low toxicity,which have a good development prospects.Most of the pyridine synthesis methods,however,require the addition of metal catalysts.So metal-catalyzed cycloisomerization,[4 + 2] cycloaddition,[3 + 3] cycloaddition,[3 + 2 + 1] cycloaddition,[2 + 2 + 2] cycloaddition,and [2 + 2 + 1 + 1] cycloaddition reactions were primarily reviewed in this paper.Secondly,we introduced the synthesis of 2,4,6-trisubstituted pyridine compounds.Poly-substituted pyridine is a kind of structural framework that is widely found in the fields of natural products,pharmaceuticals,functional materials and agrochemicals.This part presented a new method for the synthesis of poly-substituted pyridine compounds,that is,copper–catalyzed oxidative of oxime esters and glycine esters to synthesize substituted pyridines rapidly and efficiently undergo [3 + 2 + 1] cycloaddition reaction.The method has a good functional group compatibility,while the retention of ester groups on the product provides the possibility for further synthesis of pyridine derivatives.Particularly,this method provides a novel synthetic route of 2,6-symmetric substituted isonicotinate.Thirdly,we introduced the synthesis of quinoxaline compounds.This part presented a new method for the synthesis of quinoxaline compounds.The quinoxalines were successfully synthesized from 2-iodoanilines,NaN3,and 1-phenyl-2-(phenylamino)ethanones.The reaction was carried out under basic conditions using CuI as a catalyst and L-proline as a ligand.In this process,NaN3 is used as the nitrogen source to provide a nitrogen atom for the target product,thereby avoiding the formation of isomers in the conventional process using o-phenylenediamine as the substrate.