Stabilization of a putative cyclohexane-1,4-diyl intermediate elicits an antarafacial Cope rearrangement via a stepwise mechanism. Pyrolysis of (R,E)-5-methyl-1,2,6-octatriene to 4-methyl-3-methylene-1,5-heptadiene
作者:Tania Elaine Wessel、Jerome A. Berson
DOI:10.1021/ja00081a009
日期:1994.1
The pyrolysis of (E)-5-methylocta-1,2,6-triene (1) has been designed to bring to light a stepwise Cope rearrangement by stabilization of the putative biradical intermediate. Compound 1 rearranges to (E)-4-methyl-3-methylene-1,5-heptadiene ((E)-3) with the Arrhenius parameters E a =31.7 kcal/mol and log A 10.6 (A in s -1 ). (R,E)-5-Methylocta-1,2,6-triene ((R,E)-1), 90.8±0.8% enantiomerically pure,
(E)-5-methylocta-1,2,6-triene (1) 的热解旨在通过稳定假定的双自由基中间体来揭示逐步 Cope 重排。化合物 1 重排为 (E)-4-甲基-3-亚甲基-1,5-庚二烯 ((E)-3),Arrhenius 参数 E a =31.7 kcal/mol 和 log A 10.6 (A in s -1 ) . (R,E)-5-Methylocta-1,2,6-triene ((R,E)-1), 90.8±0.8% 对映体纯度,在 440 K 下热解得到 (R,E)-3,62% ee,对应于重排为 E 产物时对映体特异性的 68% 保留。因此,一个烯丙基单元的面侧参与约占反应的 16%