Electrochemical Radical–Radical Cross-Coupling Approach between Sodium Sulfinates and 2H‑Indazoles to 3‑Sulfonylated 2H‑Indazoles

A direct cross-coupling between sodium sulfinates and 2H-indazoles has been developed under electrochemical conditions. The utilization of a graphite anode and platinum cathode in an undivided cell with a constant current of 7 mA allowed the concurrent oxidations of sulfinates and 2H-indazoles to sulfonyl radical and radical cationic 2H-indazoles, facilitating the direct radical–radical coupling strategy to 3-sulfonylated 2H-indazole derivatives. The transition-metal- and redox-reagent-free synthetic approach should serve as a valuable synthetic tool to achieve heteroaromatic compounds.本工作开发了一种电化学条件下亚磺酸钠(sodium sulfinates)与2H-吲唑(2H-indazoles)的直接交叉偶联合成方法。该反应体系采用石墨阳极(graphite anode)与铂阴极(platinum cathode)组装无分隔电解池(undivided cell)，并施加7 mA恒定电流，可同时将亚磺酸盐与2H-吲唑氧化为磺酰自由基(sulfonyl radical)与自由基阳离子型2H-吲唑(radical cationic 2H-indazoles)，进而通过直接自由基-自由基偶联(radical–radical coupling)策略得到3-磺酰基化2H-吲唑衍生物(3-sulfonylated 2H-indazole derivatives)。该无需过渡金属及氧化还原试剂的合成方法，可作为构建杂芳族化合物的极具价值的合成工具。