The Application Of Direct Electrochemical Oxidation In The Synthesis Of Nitrogen-containing Heterocyclic Derivatives

It is an essential subject in the field of organic methodology to develop a green,mild and efficient electrochemical synthesis strategy.In this paper,based on direct electrolysis method,the construction of C-C bond,C-N bond and C-O bond were achieved from nitrogen-containing heterocyclic compounds.The reaction mechanism was studied in detail through cyclic voltammetry experiment and density functional theory calculation.The specific research contents are as follows:1.An Oxidant-and Catalyst-Free Electrooxidative Cross-Coupling Approach to 3-Tetrahydroisoquinoline Substituted CoumarinsA direct electrooxidative cross-dehydrogenative-coupling(CDC)reaction between N-aryl-tetrahydroisoquinolines and 4-hydroxycoumarins has been developed.This protocol provides a green,mild and fast method to construct 3-tetrahydroisoquinoline substituted coumarins in the absence of any catalyst and exogenous-oxidants.A variety of N-aryl-tetrahydroisoquinolines and 4-hydroxycoumarins are compatible with this transformation to give the corresponding products in moderate to excellent yields.Moreover,the results of control experiments,cyclic voltammetry experiments,and density functional theory(DFT)calculation indicated that the electrooxidative CDC reaction might involve in both of radical coupling and nucleophilic addition processes.2.A Green and Efficient Route Towards Pyrazole Substituted Tetrahydroisoquinolines by Convergent Paired ElectrolysisA sustainable,fast and efficient convergent paired electrolysis method for the synthesis of 1-pyrazole substituted tetrahydroisoquinolines has been developed.The protocol featured high atom and energy economy,providing a powerful tool to afford 30 substituted tetrahydroisoquinolines with high yields(80-99%)in 60-80 min.108% Faradaic efficiency could be realized.The reaction proceeded with transition metal catalyst-and chemical oxidant-free conditions,and was amenable to gram-scale synthesis in a good yield(84%).A series of mechanism studies revealed that the electrooxidative reaction might involve in two pathways: radical coupling and nucleophilic addition reactions.3.An efficient direct electrolysis method for the synthesis of 1,1,1,3,3,3-hexafluoroisopropyxy substituted imidazolo [1,2-a] pyridineA sustainable and efficient electrochemical functionalization of imidazo[1,2-a]pyridine that employs 1,1,1,3,3,3-hexafluoropropan-2-ol(HFIP)as solvent and reactant has been developed.The reaction proceeded with no metal catalysts and obtained a series of new compounds in moderate to good yields.The mechanism study indicated that the reaction might involve the radical pathway.4.A Green Electrochemical Off-On Method for Pyrimidin-2(1H)-ones Synthesis via Three-component CyclizationA green and simple ‘one-pot’ electrochemical off-on approach to pyrimidin-2(1H)-ones was realized without any catalyst,oxidant and toxic reagent.The desired products were obtained in moderate to good yields after stepwise ‘one-pot’ reaction.The results of control experiments and cyclic voltammetry indicated that the electrooxidation of DHPMs might proceed via an absorption-controlled two steps of two-electron and two-proton process with radical intermediates.