1595155-29-5Relevant articles and documents
Electrophilic alkylations of vinylsilanes: A comparison of α- And β-silyl effects
Laub, Hans A.,Mayr, Herbert
supporting information, p. 1103 - 1110 (2014/02/14)
Kinetics of the reactions of benzhydrylium ions (Aryl2CH +) with the vinylsilanes H2C=C(CH3)(SiR 3), H2C=C(Ph)(SiR3), and (E)-PhCH=CHSiMe 3 have been measured photometrically in dichloromethane solution at 20 °C. All reactions follow second-order kinetics, and the second-order rate constants correlate linearly with the electrophilicity parameters E of the benzhydrylium ions, thus allowing us to include vinylsilanes in the benzhydrylium-based nucleophilicity scale. The vinylsilane H2C= C(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 H 2C=C(CH3)2 is 103 times more reactive than propene. trans-β-(Trimethylsilyl)styrene, which is attacked by electrophiles at the silylated position, is even somewhat less reactive than styrene, showing that the hyperconjugative stabilization of the developing carbocation by the β-silyl effect is not yet effective in the transition state. As a result, replacement of vinylic hydrogen atoms by SiMe3 groups affect the nucleophilic reactivities of the corresponding C=C bonds only slightly, and vinylsilanes are significantly less nucleophilic than structurally related allylsilanes. Copyright
