Folgueiras-Amador Ana A, Teuten Alexander E, Salam-Perez Mateo, Pearce James E, Denuault Guy, Pletcher Derek, Parsons Philip J, Harrowven David C, Brown Richard C D
School of Chemistry, University of Southampton, Highfield, Southampton, SO17 1BJ, UK.
Department of Chemistry, Imperial College London, White City Campus, London, W12 0BZ, UK.
Angew Chem Int Ed Engl. 2022 Aug 26;61(35):e202203694. doi: 10.1002/anie.202203694. Epub 2022 Jul 18.
Electro-reductive radical cyclisation of aryl halides affords the corresponding hetero- and carbo-cycles in an undivided flow reactor equipped with steel and carbon electrodes using an organic mediator. A dissolving metal anode is not needed, and the mediator can be employed in a sub-stoichiometric amount (0.05 equiv), increasing the practical utility of cathodic radical cyclisation. The methodology is applied to O-, N-, and C-tethers, yielding tricyclic fused and spiro systems. In the absence of mediator, the major pathway is hydrogenolysis of the C-X bond, a 2 e process occurring at the cathode. Predominance of the radical pathway in presence of a strongly reducing mediator (M) is consistent with homogeneous electron-transfer in a reaction layer detached from the cathode surface, where the flux of M leaving the electrode is such that little aryl halide reaches the cathode.
在配备有钢电极和碳电极的不分隔流动反应器中，使用有机介质，芳基卤化物的电还原自由基环化反应可生成相应的杂环和碳环。不需要溶解金属阳极，且介质可以以亚化学计量的量（0.05当量）使用，这增加了阴极自由基环化反应的实际应用价值。该方法适用于O-、N-和C-连接基，可生成三环稠合和螺环体系。在没有介质的情况下，主要途径是C-X键的氢解反应，这是一个在阴极发生的2e过程。在强还原介质（M）存在下自由基途径占主导，这与在从阴极表面分离的反应层中的均相电子转移一致，其中离开电极的M的通量使得很少有芳基卤化物到达阴极。
