Synthesis Of Benzoxazole And Quinazolinone Derivatives Based On Photoelectrochemical Method

Benzazole(benzoxazole,benzimidazole,benzothiazole)and theirs derivatives and quinazolinone are important nitrogen-containing heterocyclic compounds.The skeletons of benzazole and quinazolinone exist in a variety of natural products and biologically active compounds.They have significant pharmacological and biological activities.Among them,2-arylquinazolinone derivatives have sedative,hypnotic,anticonvulsant,anti-depressant,anti-anxiety and other effects.In recent years,due to the advantages of photocatalytic reaction and electrochemical synthesis with mild reaction conditions,environmental protection and simple operation,they have become the future development trend of organic synthesis to gradually replace traditional organic synthesis methodsThe synthesis of benzazole derivatives generally requires oxidant/catalyst and higher reaction temperature,which does not conform to the concept of green chemistry.Therefore,a method of direct electrochemical oxidative cyclization to synthesize benzazole derivatives was developed by using o-aminophenol/o-aminothiophenol/o-phenylenediamine and aldehyde as raw materials.The optimum conditions for the synthesis of benzazole derivatives were determined by screening electrolyte,electrode material,current,solvent and reaction time:using graphite electrode(C)as anode and platinum plate electrode(Pt)as cathode,electrolyze in CH₃CN solution containing 0.1M NH₄Cl at a constant current of 2.0 m A for 2 h at room temperature.Under these conditions,the applicability of the reaction was explored,and 35 2-substituted benzazole products were obtained and their structures were characterized.In order to prove the practical potential of this method,the drug thiabendazole was synthesized on a gram scale,and the mechanism of the reaction was explored and confirmed by experiments.This reaction has the advantages of environmental protection and atomic economy.2-Arylquinazolinone derivatives are usually synthesized through the cyclization and oxidation of intermediate 2-(benzylideneamino)benzamide,which requires catalysts,oxidants and high temperature conditions.In this paper,a photocatalytic radical quinazolinone 2-arylation reaction was developed by using aryl tetrafluoroborate diazonium salt as the aryl source.The optimum conditions of the reaction were determined by screening photocatalyst and its concentration,solvent,reaction time and light source:using 2 mol%Eosin Y as the catalyst,DMSO as the solvent,and irradiating the blue LED for 6 h.Under these conditions,a total of 202-arylquinazolinone derivatives were synthesized,and their structures were characterized and confirmed.The reaction mechanism was investigated and proved to be radical reaction mechanism.The reaction is easy to operate and can be reacted at room temperature under mild conditions.