碳氮键参与的电化学阴极还原反应研究进展

Advances in Electrochemical Cathodic Reductive Reactions Involving Carbon-Nitrogen Bonds

含有碳氮键的化合物如胺、亚胺、腈与氮杂芳环等广泛存在于自然界中,并在药物、农药和材料等领域中发挥关键作用,研究碳氮键参与的反应具有重要意义.在有机合成反应中,利用碳氮键的还原反应可以脱除保护基、实现官能团转化和构建生物活性分子等.然而碳氮键特别是碳氮单键通常具有一定的化学稳定性,导致碳氮键还原反应往往需要在苛刻的条件下进行.近年来,随着有机电化学合成研究的兴起,采用温和的电化学反应途径选择性地还原碳氮键受到了研究者的更多关注.根据底物结构的不同,碳氮键参与的电化学阴极还原反应可以分为饱和碳氮键和不饱和碳氮键参与的阴极还原反应两大类.含饱和碳氮键的化合物如铵盐、酰胺、氮丙啶和硝基化合物等,其阴极还原反应涉及碳氮键的断裂和官能团的取代.含不饱和碳氮键的化合物如亚胺、肟和氮杂环等,通常会被还原为碳氮单键中间体随后发生加成.简要综述了上述两大类底物的阴极还原反应,并总结了可能的反应机理.

Compounds containing carbon-nitrogen bonds,such as amines,imines,nitriles,and N-heterocycles,are widespread in nature and play essential roles in pharmaceuticals,pesticides,materials,and other fields.The investigation of reactions involving carbon-nitrogen bonds is of paramount significance.In organic synthesis,the reduction of carbon-nitrogen bonds can be used for the removal of protecting groups,conversion of functional groups,and construction of biologically active molecules.However,carbon-nitrogen bonds,especially carbon-nitrogen single bonds,are renowned for their notable stability,thus requiring the harsh conditions for their reductions.As the renaissance of organic electrosynthesis in recent years,the electrochemical cathodic reductive reactions of carbon-nitrogen bonds under mild conditions have garnered considerable attention.According to the molecular structure of the substrates,electrochemical cathodic reductive reaction involving carbon-nitrogen bonds can be classified into two major categories:reductions of saturated carbon-nitrogen bonds,and unsaturated carbon-nitro-gen bonds.For compounds with saturated carbon-nitrogen bonds,such as ammonium salts,amides,aziridines,and nitro compounds,their cathodic reductions usually involve the cleavage of carbon-nitrogen bonds and substitution of the N-contained functional group.Compounds with unsaturated carbon-nitrogen bonds,such as imines,oximes,and N-heterocycles,are typically reduced into intermediates containing carbon-nitrogen single bonds,followed by addition reactions.A concise overview of the cathodic reductive reactions of above two kinds of substrates is provided and the possible reaction mechanisms is summarized.