On the role of pre- and post-electron-transfer steps in the SmI2 /amine/H(2)O-mediated reduction of esters: new mechanistic insights and kinetic studies.
On the role of pre- and post-electron-transfer steps in the SmI2 /amine/H(2)O-mediated reduction of esters: new mechanistic insights and kinetic studies.
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DOI：
10.1002/chem.201400295
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发表时间：
2014-04-07
影响因子：
4.3
通讯作者：
Procter, David J.
中科院分区：
文献类型：
--
作者：
Szostak, Michal;Spain, Malcolm;Procter, David J.
SmI2介导的还原未活化的酯的机制进行了研究，使用动力学，自由基时钟和反应性实验的组合。动力学数据表明，所有的反应组分（Sm I2，胺，H2O）参与的速率方程和电子转移是促进由布朗斯特碱辅助的去质子化的过渡态的水。使用验证的环丙基含自由基时钟表明，反应发生通过快速，可逆的第一电子转移，和简单的Sm（II）配合物的脂肪族酯的电子转移是快速的。值得注意的是，本文提出的机理的细节表明，SmI2，H2O和胺之间的络合提供了一类新的结构多样的，功能强大的还原剂有效的电子转移到羧酸衍生物作为一个有吸引力的替代经典的环糊精介导的减少和作为一个来源的酰基自由基等价物的C=C键形成过程。
The mechanism of the SmI2-mediated reduction of unactivated esters has been studied using a combination of kinetic, radical clocks and reactivity experiments. The kinetic data indicate that all reaction components (SmI2, amine, H2O) are involved in the rate equation and that electron transfer is facilitated by Brønsted base assisted deprotonation of water in the transition state. The use of validated cyclopropyl-containing radical clocks demonstrates that the reaction occurs via fast, reversible first electron transfer, and that the electron transfer from simple Sm(II) complexes to aliphatic esters is rapid. Notably, the mechanistic details presented herein indicate that complexation between SmI2, H2O and amines affords a new class of structurally diverse, thermodynamically powerful reductants for efficient electron transfer to carboxylic acid derivatives as an attractive alternative to the classical hydride-mediated reductions and as a source of acyl-radical equivalents for C=C bond forming processes.
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