Study On N-S And N=P Coupling Reactions Via Acyl-nitrene Intermediates

The framework structure of amide is an essential structural unit,which is widely used in the fields of organic synthesis,biomedicine,and polymer materials.Therefore,it is of great significance to develop efficient methods for amidation reaction.Transition metal catalyzed direct amidation via acyl-nitrene intermediate has become one of the important methods for the construction of amides.However,such reactions usually rely on iridium,rhodium,ruthenium and other precious metal catalysts.Cheap,readily available,and environmentally friendly metal ferric salts and titanium dioxide for direct amidation have not been reported so far.In this paper,visible-light induced iron-catalyzed S-H amidation of dioxazolones compounds with aryl thiophenols and TiO₂-catalyzed synthesis of phosphoimides from dioxazolones and triaryl phosphine were developed,respectively.The main contents were shown as below:（1）Visible-light promoted iron-catalyzed S-H amidation of arylthiophenols with3-aryl-1,4,2-dioxazol-5-ones for the synthesis of sulfonamides was studied.Through the investigation of catalyst,solvent,reaction time,wavelength and other conditions,the best reaction condition as follows:Fe Br₃ as catalyst,acetonitrile as solvent,10 W 450 nm LED as lamp source,reaction under nitrogen protection for 16 hours,the maximum yield of 88%.The results of substrate expansion showed that 1,4,2-dioxazol-5-ones substituted by aromatics,heteroaromatics and viscous cyclic aromatics were tolerated in this reaction,and good yields were obtained.The structure of the product was characterized by ¹H NMR and ¹³C NMR.（2）Visible-light promoted TiO₂-catalyzed the synthesis of phosphonimides from triphenyl phosphines and 3-aryl-1,4,2-dioxazol-5-ones was also studied.Through the investigation of catalyst,solvent,and reaction time,the optimum reaction condition was as follows:TiO₂ as catalyst,dichloromethane as solvent,12 W blue LED as lamp source,and room temperature for24 hours.The maximum yield was up to 98%.Aryl,heteroaryl and polycyclic aryl substituted1,4,2-dioxazol-5-ones were tolerated in this reaction and satisfactory yields were obtained.The structure of the product was characterized by ¹H NMR and ¹³C NMR.The reaction has some advantages such as mild condition,green process,and high efficiency.