Effects of Bridgehead Metalloidal Substituents (MMe<sub>3</sub>, M = Si and Sn) on the Stability of the 1-Norbornyl Cation
作者:William Adcock、Christopher I. Clark、Carl H. Schiesser
DOI:10.1021/ja961870c
日期:1996.1.1
corresponding values in the bicyclo[2.2.2]octane and adamantane ring systems (2, Y = OSO2Me, and 3, Y = Br, respectively) indicates the substrate order of these effects is 1 > 2 ≫ 3. Qualitative considerations lead to the pronounced effects in 1 being ascribed to “back-lobe” through-space effects (homohyperconjugation). A more quantitative picture of the stabilizing effects of SiMe3 and SnMe3 on the 1-norbornyl
4-准金属(MMe3,M = Si 和 Sn)-取代的双环 [2.2.1] 庚基-1-基三氟甲磺酸酯(1,Y = OSO2CF3)已被合成,并且它们在乙醇水溶液和三氟乙醇中的溶剂分解已经与那些母体和甲基衍生物(1,Y = OSO2CF3;X = H 和 Me,分别)。对于准金属取代基观察到大的速率增强因子。将这些加速效应与双环 [2.2.2] 辛烷和金刚烷环系统(分别为 2,Y = OSO2Me 和 3,Y = Br)中的相应值进行比较表明,这些效应的底物顺序是 1 > 2 ≫ 3. 定性考虑导致 1 中的显着效果被归因于“背瓣”空间效应(同超共轭)。通过高级 ab initio (MP2/6-31G(d)[DZP]) 分子轨道计算,描绘了 SiMe3 和 SnMe3 对 1-降冰片基阳离子 (5) 的稳定作用的更定量图片。该计算为同超共轭稳定提供了强有力的支持。