Chong Daesung, Stewart Michael, Geiger William E
Department of Chemistry, University of Vermont, Burlington, Vermont 05405, USA.
J Am Chem Soc. 2009 Jun 17;131(23):7968-9. doi: 10.1021/ja9032296.
An electrochemical process is described for the rapid and efficient conversion of unsubstituted cyclic olefins into cycloaddition products. When a potential of 1.25 V vs ferrocene was applied to a solution of cis-cyclooctene (COE) in dichloromethane/[NBu(4)][B(C(6)F(5))(4)] containing a catalytic amount (4 mol %) of ReCp(CO)(3), 1, the olefin was converted to a diastereomeric mixture of the C(8)-dimer tricyclohexadecane, with the major isomer having a cis-anti-cis geometry. Smaller cyclic olefins (C(5) to C(7)) also formed cycloaddition products. The cyclization reactions require the electrogeneration of 1(+) as an electron-transfer mediator which triggers the one-electron oxidation of the olefin in spite of the fact that the potentials of the latter lie at considerably higher values. The very low coulomb count required (ca. 0.1 F per olefin) for the conversion of olefin to product is consistent with a radical-chain mechanism. The electrochemical conversion of COE to cyclized products is complete in a few minutes, in contrast to the week-long photochemical processes previously needed for preparation of the same cycloaddition products.
描述了一种电化学过程，用于将未取代的环烯烃快速有效地转化为环加成产物。当相对于二茂铁施加1.25 V的电势至顺式环辛烯（COE）在含有催化量（4 mol%）的ReCp(CO)₃（1）的二氯甲烷/[NBu(4)][B(C₆F₅)₄]溶液中时，烯烃转化为C₈-二聚体三环十六烷的非对映体混合物，主要异构体具有顺式-反式-顺式几何结构。较小的环烯烃（C₅至C₇）也形成环加成产物。环化反应需要电生成1⁺作为电子转移介质，尽管烯烃的电势处于相当高的值，但它仍能引发烯烃的单电子氧化。烯烃转化为产物所需的极低库仑数（约每烯烃0.1 F）与自由基链机理一致。与之前制备相同环加成产物所需的长达一周的光化学过程相比，COE电化学转化为环化产物在几分钟内即可完成。
