Abstract
The compound VsiSiMe2I [Vsi =(Me3Si)2C(SiMe2CHCH2)](1) is very similar in reactivity to (Me3Si)3CSiMe2I (2) in reactions with methanol and with alkali-metal salts in MeOH or MeCN, but (1) is much the more reactive towards electrophiles which induce rate-determining ionization of the Si–I bond, viz. CF3CH2OH (the factor f is > 500), CF3CO2H (f > 1 800), AgBF4 in CH2Cl2(f ca. 150), or AgSCN in CH2Cl2(f > 500). The large differences are attributed to anchimeric assistance by the γ-vinyl group to the leaving I– under the influence of the electrophile, leading to formation of a 1,3 vinyl-bridged cation. In accord with this, reactions of VsiSiEt2I with AgBF4 or AgO2CCF3 in CH2Cl2 give ca. 1 : 2 mixtures of unrearranged and rearranged products, VsiSiEt2Y and (Me3Si)2C(SiEt2CHCH2)(SiMe2Y)(Y = F or O2CCF3). Anchimeric assistance by the γ-vinyl group is much greater than that by a γ-Me group but much smaller than that by a γ-OMe group. The chloride VsiSiEt2Cl reacts with AgO3SCF3 in CH2Cl2 by loss of the vinyl group (with anchimeric assistance by the γ-Cl atom), apparently to give a chlorine-bridged cation, and hence a mixture of the unrearranged (Me3Si)2C(SiEt2Cl)(SiMe2O3SCF3) and the rearranged (Me3Si)2C(SiEt2O3SCF3)(SiMe2Cl).
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