Cobalt Macrocycle-Catalyzed Electrochemical Coupling Reactions

在亲电试剂的存在下，双卤代物的电化学还原对于合成单取代和双取代材料有几个缺点（化学选择性和立体选择性差）。该过程将用钴(I)大环配合物催化，包括维生素B12、钴双水杨基乙二胺和钴肟。该策略是将钴物种减少到活性Co(I)状态，预计将在介质中与双卤代物进行快速氧化加成。所得到的加合物Co（III）将在原位还原，以排出所需的碳离子，与介质中的亲电试剂反应。实际上，钴大环将催化双卤化物还原为相应的-卤代碳离子。预期催化过程比直接电化学过程具有更高的立体选择性和化学选择性，并允许直接过程根本不可能发生的转化。此外，在Co(I)发生氧化加成但Co（III）加合物稳定的电位下进行电解，将有可能通过后者的热分解或光化学分解产生自由基。将根据这些原理进行许多合成应用，包括双卤代化合物（包括开链和环体系）的还原亲电取代，取代环丙烷、芳烃和多环体系的合成，以及烯烃的合成。这些原理将进一步扩展到从烷基卤化物以外的底物电催化生成碳离子。有机合成计划支持这项研究，以开发钴大环催化的电化学偶联反应。这项研究将为合成有用的反应性中间体开辟一条新的途径，可用于合成我们经济中需要的日益复杂的物质。

The electrochemical reduction of geminal dihalides in the presence of electrophilic reagents has several disadvantages (poor chemoselectivity and stereoselectivity) for the synthesis of mono-and bis-substituted materials. The process will be catalyzed with cobalt (I) macrocyclic complexes, including vitamin B12, cobalt bis-salicylideneethylenediamine, and cobaloximes. The strategy is to reduce the cobalt species to the reactive Co(I) state, which is expected to undergo rapid oxidative addition with a geminal dihalide in the medium. The resulting adduct, a Co(III) species, will be reduced in situ to eject the desired carbanion for reaction with an electrophile in the medium. In effect, the cobalt macrocycle will catalyze the reduction of the geminal halide to the corresponding alpha-halocarbanion. The catalytic process is expected to occur in far higher stereoselectivity and chemoselectivity than the direct electrochemical process, and permit conversions not possible at all by the direct process. Furthermore, by carrying out the electrolysis at potentials where oxidative addition to Co(I) takes place but the Co(III) adduct is stable, it will be possible to make radicals by thermal or photochemical decomposition of the latter. A number of synthetic applications, including reductive electrophilic substitution on geminal dihalides (including both open chain and cyclic systems), synthesis of substituted cyclopropanes, arenes, and polycyclic systems, and synthesis of alkenes, based on these principles, will be undertaken. These principles will be further extended to electrocatalytic generation of carbanions from substrates other than alkyl halides. The Organic Synthesis Program is supporting this research to develop cobalt macrocycle-catalyzed electrochemical coupling reactions. This research will lead to a new and novel route to synthetically useful reactive intermediates that can be used to synthesize the increasingly complex substances needed in our economy.