Organoselenium Reagents-mediated Synthesis Of Dihydrofuran And Pyrrolo[2,1-a] Isoquinoline Compounds

Since the first organic selenium compound diethyl selenide was prepared by L(?)wig in 1836,organoselenium reagents have gradually attracted the attention of chemists.With the continuous deepening of research on organoselenium reagents,organoselenium chemistry has become an important research hotspots and frontier areas.Nowadays,selenium compounds have been widely used in many fields including organic synthesis,biochemistry,xerography,conductive materials,semiconductors,and coordination chemistry.Among organoselenium reagents,selenium reagents with valence higher than two are widely used in organic synthesis.On the one hand,electrophilic organoselenium reagent can undergo stereospecifically anti-electrophilic addition with carbon-carbon double bond to form an active positive trivalent seleniranium ion intermediate.When nucleophilic reagents attack the seleniranium ion intermediate,anti-adducts or cyclic compounds are generated;on the other hand,selenium ylide reagent is also an importantly active trivalent selenium positive ion intermediate,which can undergo 1,3-dipole cycloaddition reaction to prepare a variety of biologic-ally active heterocyclic compounds.In this paper,the seleniranium ion and selenium ylide intermediates-mediated cyclization reactions and their application in the synthesis of dihydrofuran and pyrrolo[2,1-a]isoquinoline compounds are studied.Phenylselenyl chloride and iodobenzene were generated in situ via the reaction of diphenyl diselenide with dichloroiodobenzene in acetonitrile.Then,the intramolecular electrophilic exo-cyclization and selenofunctionalization of?-C(sp~3)atom of 1,3-dicarbonyl compounds with phenylselenyl chloride at room temperature afforded phenylseleno-substituted and bisphenylseleno-substituted dihydrofuran compounds.Furthermore,the bisphenylseleno-substituted dihydrofuran compounds can be rearranged with the assistance of iodobenzene to form bisphenylseleno-substituted dihydropyran compounds.The advantages of this method include easy operation,mild reaction conditions,good yields,and high regiospecificity.It is worth mentioning that the more stable and easily available diphenyl diselenide was used as the substrate in this reaction to generate phenylselenyl chloride in situ can effectively avoided using toxic chlorine and yielding toxic hydrogen chloride by-product gas in the preparation of phenyl selenium chloride,which undoubtedly makes the experimental operation safer and easier.Moreover,by optimizing experimental conditions,raw material ratios and using 1,3-dicarbonyl compounds with different structures,dihydrofuran and dihydropyran compounds can be obtained in good yields.A selenium ylide reagent,methylphenylvinyl selenium tetrafluoroborate was prepared.In the presence of 1,4-Diazabicyclo[2.2.2]octane,isoquinoline,2-bromoac-etylene,and the selenium ylide reagent underwent 1,3-dipolar cycloaddition reaction to afford pyrrolo[2,1-a]isoquinoline derivatives in moderate to good yield and with high regioselectivity.The advantages of this one-pot synthetic method include mild reaction conditions,easy operation,convenient separation and purification of the products,and high regioselectivity.