Substituent Effects on the Stereochemistry in the [2 + 2] Photocycloaddition Reaction of Homobenzoquinone Derivative with Variously Substituted Alkenes and Alkynes
作者:Ken Kokubo、Hiroshi Yamaguchi、Tatsuya Kawamoto、Takumi Oshima
DOI:10.1021/ja025593n
日期:2002.7.1
correlated with a combination of Taft's steric factor E(s) and the energy gain (DeltaE') associated with the orbital interactions between the spin centers of 1,4-biradicals. These results were interpreted in terms of Griesbeck's SOC mechanism as well as the possible bond rotation around the armed radical chain. Therefore, it is concluded that a balance of repulsive steric hindrance and the attractive FMO
用不同取代的烯烃和炔烃辐照同苯醌衍生物产生 [2 + 2] 光环加合物,三环二酮,几乎定量地作为区域异构体和立体异构体的混合物。所有反应的优选区域异构体归因于更稳定的 1,4-双自由基中间体(主要加成模式),而次要异构体归因于不太稳定的双自由基(次要加成模式)。使用苯硒醇的自由基捕获实验证明了这两种区域异构双自由基的产生,反映了无硒醇光反应的区域选择性。两种双自由基倾向于优先产生具有较小取代基如乙氧基、氰基和乙酰氧基的烯烃的内异构体,但具有较大取代基如苯基、咔唑基和叔丁基的烯烃的外异构体。对数外/内比与 Taft 的空间因子 E(s) 和能量增益 (DeltaE') 的组合密切相关,该能量增益 (DeltaE') 与 1,4-双自由基的自旋中心之间的轨道相互作用有关。这些结果是根据 Griesbeck 的 SOC 机制以及围绕武装激进链的可能键旋转来解释的。因此,可以得出结论,排斥性位阻和有吸引力的