Study On The Electrochemical Oxidation Of Carbon Heterobonds

With the development of modern society,resource shortages and environmental pollution has become a big scientific issue.The exploration of green and sustainable ways for the construction of high value-added chemical products has become an important research field in modern organic synthesis.Oxidative cross-coupling using two nucleophiles as starting materials to solve the problem that traditional cross-coupling reactions require the pre-functionalization steps of substrates,which provides a new method to construct chemical bonds.However,in general,the external oxidant is essitial for oxidative cross-coupling process,which leads to the difficult purification from undesired byproducts and decreases the atom economy of the whole transformation.An ideal reaction mode for oxidative cross-coupling pathway is using readily available substrates with hydrogen evolution.Organic electrosynthesis is recognized as an attractive method that employs inexpensive and safe electrons as the "mass-free reagent"not only achieve the oxidative cross-couplings under external-oxidant-free conditions,but also release valuable hydrogen gas during the chemical bond formation,which provides new opportunities for synthesis of organic compounds in a green and efficient way.In this doctoral dissertation,the history and development of electrochemistry and oxidative cross-coupling reaction were introduced.Then,the development of electrochemical oxidative carbon-heteroatom(C-O,C-N,C-S,C-P,C-Se)bonds formation was reviewed.Our research mainly focused on the environmentally friendly carbon-heteroatom bonds formation under electrochemical oxidative conditions.By screening the factors of solvents,electrodes,electrolytes,current and additives,several carbon-heteroatom bonds formation without transition metal and external oxidant were realized under electrochemical conditions.In order to get more insights into the possible mechanism of these transformation,a series of radical trapping experiments and cyclic voltammetry were conducted and the electrochemical process under different conditions was described.These results provided a theoretical basis for exploring the green and convenient carbon-heteroatom bonds formation.The main research contents and innovative results are as follows:(1)An electrochemical intermolecular cyclization between ?-keto acids and acylhydrazines has been developed for the synthesis of 2,5-disubstituted 1,3,4oxadiazoles with the yields up to 91%.This transformation proceeded smoothly under mild reaction conditions without external oxidant,base and transition metal catalyst.Both symmetrical and unsymmetrical 2,5-disubstituted 1,3,4-oxadiazoles were obtained with different substrates.Gram-scale synthesis also showed the application potential of this protocol.(2)An electrochemical oxidative C(sp2)-H sulfuration has been developed.This transformation proceeded smoothly under mild reaction conditions without external oxidant and transition-metal catalyst.Remarkably,thiophenols were selectively coupled with enamines even the substrates had other alkenyl groups.In addition,the desired products were further transformed into a series of ?-sulfur isoxazoles,which was a kind of useful heterocycles in materials and bioactive molecules.(3)A highly stereoselective synthesis of thiocyanated enaminones was achieved by electrochemical process,which involved C-H bond thiocyanation and vinyl C-N bond transamination.By using an inexpensive and stable ammonium thiocyanate as both thiocyanation reagent and supporting electrolyte,the reaction was compatible with a series of enaminones without external oxidant,supporting electrolyte and transition-metal catalyst.Gram-scale synthesis showed the potential of this protocol for practical application.(4)An electrochemical radical cascade oxythiolation of olefinic amides with thiophenols or diselenides has been developed.This method showed an efficient and practical synthesis of arylthio and selenium tethered benzoxazine derivatives and iminoisobenzofurans under mild conditions without external oxidant and transition-metal catalyst.Furthermore,this radical cascade reaction provided a simple method for the construction of C-O and C-S bonds in one step...