Photo/Electrochemical Synthesis Of 1,2,4-Triazolidines With Azobenzenes

Nitrogen heterocyclics have a wide range of applications in the fields of natural products,materials science and biochemistry,and 1,3-dipolar cycloaddition reaction is one of the most important and effective methods for constructing heterocyclic compounds.For a long time,1,3-dipolar cycloaddition reactions are usually catalyzed by metal Lewis acids or strong organic acids such as trifluoroacetic acid,but there are few reports on reactions under visible light photocatalysis/electrochemical conditions.Because the direct conversion of N=N bonds of azobenzenes is quite difficult,its research lags behind for a long time.In previous studies,a series of nitrogen heterocyclic compounds were be effectively synthesized by transition metal-catalyzed cascade ortho-C–H activation/cyclization with N=N bond as the directing group.Therefore,it is important to develop an economical and efficient method to realize the direct transformation of N=N bonds of azobenzene.The [3+2] cycloaddition reaction is an effective method for the synthesis of fivemembered rings,and the development of photo/electrochemistry in organic synthesis provides new opportunities for it.In this thesis,the photo/electrochemical synthesis of1,2,4-triazolidines with azobenzenes were studied,mainly including:(1)The [3+2] cycloaddition reaction of azobenzenes and dimethylamines mediated by visible light was realized.The reaction uses rose bengal as a photocatalyst and irradiates the acetonitrile solution of azobenzene and N-(methoxymethyl)-N-(trimethylsilylmethyl)benzylamine with 15 W green LEDs at room temperature to obtain the target compound.The reaction did not use metal catalyst.It features the mild conditions and good substrate applicability.A series of 4-alkyl-1,2-diaryl-1,2,4-triazolidines were obtained with excellent yields.It overcomes the defect that the 4-substituent can only be aryl in our previously reported method for the synthesis of 1,2,4-triazolidines,and provides a new method for the synthesis of 1,2,4-triazolidines.(2)The [3+2] cycloaddition reaction of azobenzenes and dimethylamine were explored by electrochemical synthesis strategy.Under the conditions of no external catalyst and constant current electrolysis,the reaction of azobenzene with N-(methoxymethyl)-N-(trimethylsilylmethyl)benzylamine was carried out smoothly using tetrabutylammonium tetrafluoroborate as electrolyte.A series of azobenzenes and N-(methoxymethyl)-N-(trimethylsilylmethyl)alkylamines showed good tolerance.The reaction time is short and the condition is mild.The application of Organic electrosynthesis strategy provides the possibility for the follow-up industrial synthesis of1,2,4-triazolidines.The work enriched the methods for synthesis of 1,2,4-triazolidines.