Reactions of SmI2 with alkyl halides and ketones:: Inner-sphere vs outer-sphere electron transfer in reactions of Sm(II) reductants
Reactions of SmI2 with alkyl halides and ketones:: Inner-sphere vs outer-sphere electron transfer in reactions of Sm(II) reductants
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DOI：
10.1021/ja001260j
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发表时间：
2000-08-16
影响因子：
15
通讯作者：
Flowers, RA
中科院分区：
文献类型：
--
作者：
Miller, RS;Sealy, JM;Flowers, RA
本文介绍了添加剂的影响的SmI 2介导的卤代烷和酮的偶联的机制和选择性。1-碘丁烷和2-辛酮的反应进行了与SmI 2在无助溶剂和存在下的HMPA，LiBr，和LiCl。使用无助溶剂的SmI_2和SmI_2-HMPA还原剂的实验得到Barbier产物，主要是5-甲基-5-十一醇。用LiBr作为添加剂进行的相同程序仅产生频哪醇产物7，8-二甲基-7，8-十四烷醇。还进行了在LiBr、LiCl和HMPA存在下SmI 2介导的1-碘代二烷和2-辛酮偶联的仔细产物分析。SmI 2和LiBr的组合再次仅产生频哪醇偶联产物，并且留下未还原的1-碘代十二烷。相比之下，SmI 2-HMPA组合仅产生Barbier产物。Sm（II）还原剂采用循环伏安法和紫外-可见光谱分析加上反应协议的变化和机制的研究导致的结论是，SmI 2介导的耦合的烷基卤和羰基的存在下，HMPA通过外层电子转移过程给出了巴比尔产品，而利用SmI 2的反应。与LiBr或LiCl反应，通过酮的内层还原偶联得到频哪醇产物。本文提出的结果表明，它是可能的，以改变Sm（I）试剂的反应性和选择性，通过选择添加剂或共溶剂，主要是通过改变还原剂周围的空间体积。
This paper presents the effect of additives on the mechanism and selectivity of the SmI2-mediated coupling of alkyl halides and ketones. The reaction of 1-iodobutane and 2-octanone was carried out with SmI2 in the absence of cosolvent and in the presence of HMPA, LiBr, and LiCl. The experiments using cosolvent free SmI2 and SmI2-HMPA reductants gave the Barbier product, 5-methyl-5-undecanol predominantly. The same procedure carried out with LiBr as an additive produced the pinacol product, 7,8-dimethyl-7,8-tetradecanediol, exclusively. A careful product analysis of the SmI2-mediated coupling of 1-iodododccane and 2-octanone in the presence of LiBr, LiCI, and HMPA was also performed. The combination of SmI2 and LiBr again produced the pinacol coupling product exclusively and left the 1-iodododecane unreduced. In contrast, the SmI2-HMPA combination gave only the Barbier product. Analysis of the Sm(II) reductants employing cyclic voltammetry and UV-vis spectroscopy coupled with reaction protocol changes and mechanistic studies led to the conclusion that the SmI2-mediated coupling of alkyl halides and carbonyls in the presence of HMPA gives the Barbier product through an outer-sphere electron-transfer process, while the reaction utilizing SmI2. with LiBr or LiCl gives the pinacol product through an inner-sphere reductive coupling of ketones. The results presented herein show that it is possible to alter the reactivity and selectivity of Sm(I) reagents through the choice of additives or cosolvents, primarily by changing the steric bulk around the reductant.