Solvolysis of Cyclohexenyliodonium Salt, a New Precursor for the Vinyl Cation: Remarkable Nucleofugality of the Phenyliodonio Group and Evidence for Internal Return from an Intimate Ion-Molecule Pair
Solvolysis of (4-tert-butyl-1-cyclohexenyl)aryliodonium tetrafluoroborates was examined in alcohol and aqueous solutions at 25-70 degrees C. Phenyliodonio group was found to be a remarkably good nucleofuge with a leaving ability about 10(6) times greater than triflate. In addition to the expected solvolysis products, 1-alkoxycyclohexene and/or cyclohexanone and iodobenzene, the internal return products, (4-tert-butyl-1-cyclohexenyl)iodobenzenes, were obtained in yields of 13-15% in methanol and aqueous solutions and of 30-40% in trifluoroethanol. The ortho derivative is the predominant isomer of these products, and this isomeric distribution is taken as indicating that the return is occurring from the intimate ion-molecule pair. The formation of a free-radical product, 4-tert-butylcyclohexene (1%), was detected during the solvolysis in the presence of 1,4-cyclohexadiene or in 2-propanol, while a considerable amount of the cationic rearrangement product, cyclopentyl methyl ketone, was obtained in the solvolysis of (2-methyl-1-cyclohexenyl)phenyliodonium tetrafluoroborate. A proposed mechanism involves mainly heterolysis to give the cyclohexenyl cation-iodobenzene pair with accompanying single electron transfer (or with competing homolysis) to lead to a free radical intermediate.
Reactions of Cyclohexenyl Iodonium Tetrafluoroborate with Bromide Ion: Retardation Due to the Formation of λ<sup>3</sup>-Bromoiodane
作者:Tadashi Okuyama、Shohei Imamura、Morifumi Fujita
DOI:10.1021/jo0523013
日期:2006.2.1
The reaction of 4-tert-butylcyclohex-1-enyl(phenyl)iodonium tetrafluoroborate (1a) and the 4-chlorophenyl derivative (1b) with bromide ion was examined in methanol, acetonitrile, and chloroform. Products include those derived from the intermediate cyclohexenyl cation as well as 1-bromocyclohexene. Kinetic measurements show that the reaction of 1 is strongly retarded by the added bromide. The curved
4-反应叔-butylcyclohex -1-烯基(苯基)碘鎓四氟硼酸盐(1A)和4-氯苯基衍生物(1b中与溴离子)在甲醇,乙腈,和氯仿进行了研究。产品包括衍生自中间体环己烯基阳离子以及1-溴环己烯的产品。动力学测量表明,加入的溴化物强烈阻碍了1的反应。观察到的速率常数对溴化物浓度的曲线依赖性是典型的中间体加合物的平衡前形成的过程,该中间体加合物具有不依赖溴化物的快速反应(碘鎓离子的溶剂分解)。加合物的形成,λ 3紫外光谱的变化也证实了溴代碘。碘鎓离子的相对反应性和λ 3 -bromoiodane被评估为10的量级2。溴化物取代产物既通过游离碘鎓离子的S N 1反应形成,也通过碘烷的配体偶联形成。