Electroorganic chemistry. II. Electroreduction of vicinal dibromides
Electroorganic chemistry. II. Electroreduction of vicinal dibromides
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有机电化学。
DOI：
10.1021/jo00930a018
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发表时间：
1974
影响因子：
3.6
通讯作者：
H. R. Rogers
中科院分区：
文献类型：
--
作者：
J. Casanova;H. R. Rogers
在非常温和的条件下，在搅拌的汞阴极上电还原邻位二溴化合物可产生定量的烯烃。所得的立体化学表明，消除从反式-周面构象是强烈优选的，如果这样的构象是可访问的。尝试截取碳负离子中间体是不成功的，表明还原消除在两个反应中心是同步的或几乎是同步的。邻位二溴化物还原消除生成烯烃是一个受到有限关注的古老反应，2因为产物烯烃通常也是制备二溴化物的起始点。涉及锌的还原消除3已在甾体化学中被利用，4最近在环丁二烯二聚体的制备中被利用。5极谱研究表明，邻位二溴化物还原的半波电位与C-Br键间的二面角有显著的关系，6而产物研究表明，整个反应过程可表示如下。Br Br
Electroreduction of vicinal dibromides at a stirred mercury cathode produces quantitative yields of olefins under very mild conditions. The resulting stereochemistry suggests that elimination from the trans-periplanar conformation is strongly preferred, if such conformation is accessible. Attempts to intercept a carbanionic inter-mediate were unsuccessful, indicating that the reductive elimination is either synchronous at both reacting cen-ters or nearly so.The reductive elimination of vicinal dibromidesto pro-duce olefins is a venerable reaction which has received limited attention, 2 inasmuch as the product olefin is usu-ally also the starting point for the preparation of the dibromide. Reductive elimination involving zinc3has been exploited in steroid chemistry, 4 and more recently in the preparation of cyclobutadiene dimers. 5 Polarographic studies have shown a marked dependence of half-wave po-tential for the reduction ofvicinal dibromides on the dihedral angle betweenthe C-Br bonds, 6 and theproduct studies of this reaction7 have shown that theoverall pro-cess may be represented as follows. Br Br