作者:Y\={u}ji Yanagida、Hideo Shigesato、Masakatsu Nomura、Sh\={o}ichi Kikkawa
DOI:10.1246/bcsj.47.677
日期:1974.3
The reaction of bromine with both trans-5,6-dichloro-2-norbornene (I) and exo-cis-5,6-dichloro-2-norbornene (III) in an acetic acid solution gave trans-adducts in a 100% yield, while the bromination of endo-cisr-5,6-dichloronorbornene (II) afforded the endo-cis adduct in a ca. 100% yield. The latter observation was explained in terms of a sterical inhibition of the bromide ion’s attack in the endo-direction by the two endo-chloro substituents. In the CCl4 solution, however the reaction of I with bromine afforded the exo-cis adduct in a 64% yield, together with the trans-adduct (36% yield). Then, the reaction of I with bromine was carried out in several other solvents (CH3OH, Cl(CH2)2Cl, CH3CO2C2H5, and CCl4). As the polarity of the solvents (the ET values are used here as a measure of the solvents’ polarity) decreased, the formation of the exo-cis adduct became progressively more predominant, while the addition of bromide salt retarded the formation of the exo-cis adduct. Such results and the kinetic studies suggested that the exo-cis adduct was formed through the carbonium bromide ion-pair mechanism. The stereoisomers obtained in this study were assigned on the basis of the NMR spectra.
在乙酸溶液中,溴与反式-5,6-二氯-2-降冰片烯(I)和外-顺式-5,6-二氯-2-降冰片烯(III)反应生成反式加合物,收率为 100%,而内-顺式-5,6-二氯降冰片烯(II)的溴化反应生成内-顺式加合物,收率约为 100%。对后一种情况的解释是,两个内氯取代基抑制了溴离子在内向的攻击。然而,在 CCl4 溶液中,I 与溴反应生成了外顺式加合物,收率为 64%,同时还生成了反式加合物(收率为 36%)。随后,I 与溴的反应在其他几种溶剂(CH3OH、Cl(CH2)2Cl、CH3CO2C2H5 和 CCl4)中进行。随着溶剂极性的降低(这里用 ET 值来衡量溶剂的极性),外顺式加合物的形成逐渐变得更加主要,而溴盐的加入则延缓了外顺式加合物的形成。这些结果和动力学研究表明,外顺式加合物是通过溴化碳离子对机制形成的。本研究中获得的立体异构体是根据核磁共振波谱确定的。