Electrophilic Alkylations of Vinylsilanes: A Comparison of α- and β-Silyl Effects
作者:Hans A. Laub、Herbert Mayr
DOI:10.1002/chem.201303215
日期:2014.1.20
benzhydrylium‐based nucleophilicity scale. The vinylsilane H2CC(CH3)(SiMe3), which is attacked by electrophiles at the CH2 group, reacts one order of magnitude faster than propene, indicating that α‐silyl‐stabilization of the intermediate carbenium ion is significantly weaker than α‐methyl stabilization because H2CC(CH3)2 is 103 times more reactive than propene. trans‐β‐(Trimethylsilyl)styrene, which is attacked
benzhydrylium离子的反应(芳基的动力学2 CH +与乙烯基硅烷)H 2 CC(CH 3)(SIR 3),H 2 CC(PH)(SIR 3),和(ë)-PhCH CHSiMe 3已在20°C的二氯甲烷溶液中以光度法测量。所有反应均遵循二阶动力学,二阶速率常数与苯甲酸铵离子的亲电子参数E线性相关,因此使我们可以将乙烯基硅烷纳入基于苯甲酸铵的亲核性标度中。乙烯基硅烷ħ 2 CC(CH 3)(森达3),其是通过在亲电子CH攻击2基团,反应一个数量级比丙烯更快,表示中间碳正离子的α-甲硅烷基的稳定比α甲基稳定显著较弱因为ħ 2 CC(CH 3)2的 反应活性比丙烯高10 3倍。反式-β-(三甲基甲硅烷基)苯乙烯在甲硅烷基化位置受到亲电试剂的攻击,其反应性甚至比苯乙烯低,这表明在过渡态中,β-甲硅烷基效应对正在发展的碳正离子的超共轭稳定作用仍然无效。 。结果,SiMe 3取代了乙烯基氢原子