Cleavage of silicon–carbon bonds in tris(trimethylsilyl)methylsilicon compounds by trifluoroacetic acid. Rearrangements and anchimeric assistance
Abstract
The fairly high rate of reaction of the highly sterically hindered compound (Me3Si)3CSiMe2Ph with CF3CO2H[to give (Me3Si)3CSiMe2O2CCF3and PhH] is consistent with the view that the ratedetermining step involves the transfer of a proton from the acid to the ipso-carbon atom of the ring. The formation of the rearranged species (Me3Si)2C(SiMe2F)(SiMe2O2CCF3) in the reaction of (Me3Si)3-CSiPhMeF with CF3CO2H suggests that the leaving of benzene from the initial protonated species generates a methyl-bridged silicon cation. Treatment of(Me3Si)3CSiPhMel with AgO2CCF3–CF3CO2H gives the rearranged (Me3Si)2C(SiPhMe2)(SiMe2O2CCF3), which reacts with CF3CO2H under reflux to give (Me3Si)2 C(SiMe2O2CCF3)2. In a remarkable example of anchimeric assistance by a γ-OMe group the compound (Me3Si)3CSiMe2OMe reacts readily with CF3CO2H at room temperature with evolution of methane, and formation finally of (Me3Si)2C(SiMe2O2CCF3)2 apparently via(Me3Si)2C-(SiMe2OMe)(SiMe2O2CCF3). Sulphuric acid reacts very vigorously with (Me3Si)3CSiMe2OMe, and hydrolysis of the initial product gives the diol (Me3Si)3C(SiMe2OH)2. This diol can also be obtained by hydrolysis of (Me3Si)2C(SiMe2O2CCF3)2.