摘要/Abstract

质子耦合电子转移(PCET)是一类非传统的氧化还原反应, 因其电子和质子转移过程具有独特的相互依赖性, 这类反应表现出特殊的反应性和选择性. PCET反应在包括天然和人工系统的氧化还原过程中, 如小分子活化等, 起到了相当关键的作用. 最近, PCET反应在有机合成中的应用引起了广泛的关注和兴趣. 人们实现了通过PCET机理的X—H键(如C—H键、N—H键、S—H键和O—H键等)的活化, 基于该过程合成了多种重要结构和基础骨架、获得了不同的合成砌块和天然产物. 此外, 通过PCET反应机理, 人们不仅获得了C=Y键等多重键的还原产物, 而且获得了底物之间的偶联产物. 综述了近年来PCET在有机合成中的应用和发展, 并且对该领域未来的发展进行了展望.
关键词: 质子耦合电子转移, 有机合成, 自由基反应, 官能化
Proton-coupled electron transfer (PCET) reactions are a kind of unconventional redox reactions, which exhibit special reactivities and selectivities due to their unique interdependent electron-proton transfer mechanisms. There are three possible pathways of PCET processes, including stepwise electron transfer followed by proton transfer (ETPT), proton transfer followed by electron transfer (PTET), and concerted pathway in which electron and proton transfer synchronously (CEPT), avoiding intermediates with high energy. These reactions have been playing a key role in numerous areas in organic chemistry, inorganic chemistry, bioorganic chemistry, organometallic and material chemistry, including the redox processes in natural and artificial systems, such as the activation for small molecules. Recently, the application of PCET reactions in organic synthesis has received a great deal of attentions and interests. Being accompanied by the development of electrochemical methods and photocatalysts, more and more novel reactions in electrochemistry and photochemistry involve PCET processes have been reported. Applying these electrochemical and photochemical methods, the activation of X—H bond has been achieved via PCET processes, including C—H bond, N—H bond, P—H bond, S—H bond or O—H bond. Thus, based on these crucial processes, a number of vital structures and fundamental frameworks can be synthesized, and various synthetic building blocks and natural products have been attained. For example, pharmaceutical building blocks like 2°-piperidines can be cyanated at their α-position; substituted dimeric pyrroloindolines such as (–)-calycanthidine, (–)-chimonanthine, and (–)-psychotriasine have also been successfully synthesized via PCET mechanism. Moreover, not only the products of reduction of multiple bonds (C=Y bond such as C=C bond, C=N bond and C=O bond), but also the products of self/cross-coupling have been achieved via PCET mechanism. In this review, the recent applications and developments of PCET mechanism in organic synthesis are summarized, including new catalyst systems and new reagents, especially with electrochemical and photochemical methodologies. The future of this area has also been demonstrated from both experimental and theoretical aspects.
Key words: proton-coupled electron transfer, organic synthesis, radical reactions, functionalization


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