Electrochemical-enabled Rhodium-catalyzed [4+2] Annulations Of Arenes With Alkynes

Isoquinolinium salts and cinnolinium salts are valuable compounds.Natural products containing these structures have a variety of biological activities.After clinical trials,scientists have applied them to antibacterial,anti-inflammatory,tumors,leukemia and other diseases.In recent years,it has attracted a lot of attention,and many articles have scrambled to report the synthesis methods of related compounds.Recent years,electrochemical synthesis has received extensive attention.The advantage is that the use of toxic or dangerous oxidants and reducing agents are avoided,and the transfer of electrons is used as a redox method,which reduces the consumption of substances,and the products are easy to separate.The products have high purity and less environmental pollution.The reaction speed can be effectively and continuously changed by controlling the current and voltage,and the occurrence of side reactions can be reduced,so that the yield and selectivity of the target product are higher;the reaction can be carried out at normal temperature and normal pressure,which saves energy and reduces equipment investment.Herein,an electrocatalytic method was developed to successfully synthesize isoquinolinium salts and cinnolinium salts through the regioselective cyclization of arenes and alkynes catalyzed by current-driven rhodium.Compared with traditional methods,the strategy of combining rhodium catalysts with electrochemistry not only avoids the need for stoichiometric amounts of external oxidants,but also ensures the conversion of products under mild and green conditions,resulting in the successful synthesis of a variety of substrates with drug fragments.The product has good functional group tolerance.The substrate applicability and industrial application potential of this method were fully demonstrated through substrate expansion,scale-up experiments(decagram-scale),fluorescence spectroscopy experiments,and cell staining experiments.In addition,the electrochemical reaction is simple to operate and efficiently carried out in an air atmosphere by using an undivided electrolytic cell.Finally,the possible catalytic cycle mechanism is proposed through control experiments,x-ray photoelectron spectroscopy tests,kinetic isotope experiments,cyclic voltammetry and theoretical calculations.