On the mechanism of the selenolactonization reaction with selenenyl halides
On the mechanism of the selenolactonization reaction with selenenyl halides
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DOI：
10.1021/jo0610457
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发表时间：
2006-09-15
影响因子：
3.6
通讯作者：
Edwards, Michael G.
中科院分区：
文献类型：
--
作者：
Denmark, Scott E.;Edwards, Michael G.
本文研究了β，γ-不饱和酸及其衍生物的硒环化反应机理。本文用VT-NMR和原位红外光谱法研究了（E）-4-苯基-3-丁烯酸10及其硅酯和烷基酯与苯-烯基氯（PhSeCl）和溴（PhSeBr）的反应。而酸10在碱存在下的反应是不可再现的和复杂的，甲硅烷基酯的反应是干净的，并且在-70 ℃下自发地和定量地提供作为单一（马可夫尼科夫）异构体的氯硒化加合物。随着温度的升高，该加合物经历三个过程：（1）反转为起始材料，（2）异构化为反马氏产物，和（3）环化为硒内酯12。所有这些过程都被认为是通过硒铱离子进行的，其中间性是通过独立的合成和光谱鉴定建立的。通过交叉实验明确地建立了氯硒化物加合物的可逆形成。发现10与PhSeBr的反应是快速的，但在室温下在化学上是不利的。
The mechanism of selenocyclization reactions of beta,gamma-unsaturated acids and their derivatives has been studied. The reactions of (E)-4-phenyl-3-butenoic acid 10 and its silyl and alkyl esters with benzenese-lenenyl chloride (PhSeCl) and bromide (PhSeBr) have been examined by VT-NMR and in situ IR spectroscopic methods. Whereas the reactions of the acid 10 in the presence of a base were irreproducible and complicated, reactions of the silyl esters were clean and spontaneously and quantitatively afforded a chloroselenylation adduct at -70 degrees C as a single (Markovnikov) isomer. This adduct underwent three processes as the temperature was raised: (1) reversal to the starting materials, (2) isomerization to the anti-Markovnikov product, and (3) cyclization to the selenolactone 12. All of these processes are believed to proceed via a seleniranium ion the intermediacy of which was established by independent synthesis and spectroscopic identification. The reversible formation of chloro selenide adducts was unambiguously established by crossover experiments. The reaction of 10 with PhSeBr was found to be rapid but thermodynamically unfavorable at room temperature.