The compound (Me3Si)3CSiMeClI reacts with Hg(OAc)2 in AcOH to give (Me3Si)2C(SiMe2OAc)2, under conditions in which the chloride (Me3Si)3CSiMe2Cl is inert. Similarly, (Me3Si)2C(SiMe2OAc)2 reacts with CF3CO2H to give (Me3Si)2C[SiMe2(O2CCF3)]2 under conditions in which (Me3Si)3CSiMe2OAc is inert. The results can be accounted for in terms of anchimeric assistance by the neighbouring acetoxy or trifluoroacetoxy group to the breaking of the SiCl or SiOAc bond. © 1979.