Cross-Dehydrogenative-Coupling(CDC) Of 2-Phenylquinoxalines And Phosphonating Reagents

Quinoxalines and their derivatives are an important class of nitrogen-containing heterocyclic compounds,which are used in the fields of medicine,pesticides,dyes,and electroluminescent materials.Therefore,the functionalization of quinoxalines and derivatives has very important research value.As a kind of efficient reaction for the construction of carbon-carbon bond and carbon-heteroatom bond,cross dehydrogenation coupling(CDC)reaction has an important position in organic synthetic chemistry.Compared with the classic carbon-carbon and carbon-heteroatom bond-forming reactions,the CDC reaction has the advantages of higher atom economy,shorter experimental procedures,and more environmentally friendly.It has attaracted serious concern of chemists in recent years.In this paper,CDC reaction is applied to the new functionalization of quinoxaline derivatives,and the further application of this method in the field of organic synthesis is developed.In this paper,CDC was conducted using 2-phenylquinoxaline as the reaction substrate,diphenylphosphine oxide as the phosphonylating reagent.Subsequently,the reaction conditions were optimized.The effects of the molar ratio of raw materials,the catalyst,the oxidant and its loading,the additive and its loading,the solvent,the reaction temperature and the reaction time on the reaction were investigated.The results demonstrated that the reaction proceeded smoothly in the presence of K₂S₂O₈(1.5 equiv)with TFA(1.5 equiv)and molar ratio of the raw materials(1:2)in CH₃CN(2 mL,0.5/1.5,v/v)without transition-metal catalyst at 100 ? for 7 h providing the target product in 74%yield.A series of the different substituent phosphoquinoxaline products were synthesized under the optimized conditions.The reaction showed a good substrate scope and broad range of functional group tolerance.The successful development of this reaction system provides a new method for the synthesis of phosphoquinoxaline products,and also provides more examples for CDC reactions without transition-metal catalysts.