Electrochemically Oxidative Synthesis Of Five-membered Heterocycles Induced By Iodine Anion

Electrochemical organic synthesis constitutes a green and environmentallybenigh approach for the synthesis of organic compounds by using electrons instead ofchemical oxidant or reductant, which prevents and reduces pollution from the source.On the other hand, direct oxidative activation and functionalization of C-H bond isone of the research hotspots. It has been demonstrated that a catalytically oxidativesystem consists of catalytic amount of inorganic iodide ion and stoichiometric amountof oxidant can be used to avtivate C-H bond to synthesize heterocyclic compoundscontaining new C-O bonds or C-N bonds, which exist extensively in nutrual productsand synthetic drugs. However, utilization of stoichiometric amount of oxidant causesnot only a waste of oxidant, but also tedious isolation of product and problematicdispose of the reduced side product from oxidant. In this paper, our work includes thefollowing two parts:1) A series of2-substituted benzoxazoles was efficiently synthesized byelectrochemical oxidation of Schiff base in undivided cell, using inorganic iodide asmediator. In this process, several parameters that may influence the reaction,including type of mediator, amount of mediator, solvent, current density, electrode andso on, have been initially investigated. On the basis of the reaction conditionsopitimization, an electrochemical approach for the synthesis of2-substitutedbenzoxazoles is developed. All products are characterized by1H NMR,13C NMR andHR-MS (EI). The possible mechanism of the reaction is finally proposed. The methodhas advantages of mild reaction conditions, and excess oxidant is not required.2) After mechanism study of the electrochemical synthesis of2-substitutedbenzoxazoles, we further explored the direct amination of benzoxazoles catalyzed byiodide. Herein, we investigated the effect of type, loading of mediator, solvents,current density and electrode materials on the yield of amination reaction. Then, aseries of2-aminated benzoxazoles was synthesized under the optimized conditionsand characterized by1H NMR,13C NMR and HR-MS (EI). Finally, a possiblemechanism of the direct amination reaction was proposed. The method functions asmild reaction conditions. In addition, extral oxidant and supporting electrolyte are notrequired. It is noting that more work is still required to enlarge on the generality andscope of substrates.