Electrochemical Synthesis Of 4H-1,3-Benzoxazines,Indoles And Benzimidazolones Via Dehydrogenative Cyclization Or Annulation

Heterocycles are a class of structural skeletons that are widely found in natural products and bioactive molecules.How to synthesize such compounds more greenly and efficiently has been a hot spot for organic chemists.As a green synthesis method,more and more attention has been paid to organic electrochemistry in recent years,and it has broad application prospects in the synthesis of heterocyclic compounds.In this thesis,the synthesis of heterocyclic compounds such as 4H-1,3-benzoxazine,indole and benzimidazolone has been successfully achieved by electrochemical method without additional oxidant.In the first part,an unprecedented electrochemical aromatic C-H oxygenation reaction for the synthesis of 4H-1,3-benzoxazines from easily available N-benzylamides is reported.These oxidative cyclization reactions proceed in a transition-metal-and oxidizing reagent-free fashion and produce H2 as main theoretical byproduct.Adapting the C-H oxygenation reaction in an electrochemical microreactor has been demonstrated.In the second part,a ruthenium-catalyzed electrochemical dehydrogenative annulatio n reaction of aniline derivatives and alkynes has been developed for the synthesis of indoles.Electric current is used to recycle the active ruthenium-based catalyst and promote H2 evolution.The electrolysis reaction is operationally convenient as it employs a simple undivided cell,proceeds efficiently in an aqueous solution,and is insensitive to air.In the third part,we report on a methodology that provides highly substituted benzimidazolone derivatives by building both the benzene and the heterocyclic rings through a dehydrogenative cyclization cascade.The benzimidazolone moiety are important scaffold for pharmaceutical applications as several commercial drugs contain this structure.These bicyclic heterocycles are usually synthesized from a benzene derivative through construction of the five-membered heterocyclic ring.Readily available arylamine-tethered 1,5-enynes undergo electricity powered cascade reaction to afford functionalized benzanellated heterocycles in a single step with complete control of regiochemistry.The use of electricity to promote these dehydrogenative transformations obviates the need for transition metal-based catalysts and oxidizing reagents and allows the reactions to produce H2 as the theoretical byproduct.