| Abstract: | The finding that compounds of the type (Me3Si)2(PhMe2Si)CSiMePhX react with electrophiles to give very predominantly rearranged products (Me3Si)2(Ph2MeSi)CSiMe2Y, which would be expected to be thermodynamically disfavoured, can be rationalized in terms of a mechanism in which the anchimerically-assisted departure of X− gives the Ph-bridged cation (Me3Si)2MePh]+ which is attacked by the nucleophile at the less hindered centre bearing two Me groups rather than that bearing one Me and one Ph group, with the outcome determined by kinetic rather than thermodynamic factors. Both (Me3Si)2(Ph2MeSi)CSiMe2Br and its isomer (Me3Si)2(PhMe2Si)CSiMePhBr react with AgBF4 in CH2Cl2 or Et2O to give >95% of the fluoride (Me3Si)2(Ph2MeSi)CSiMe2F. Reaction of the bromide (Me3Si)2(PhMe2Si)CSiMePhBr with AgO2CCF3 in Et2O, and that of the hydride (Me3Si)2(PhMe2Si)CSiMePhH with ICl in CCl4, likewise give >95% of the rearranged (Me3Si)2(Ph2MeSi)CSiMe2O2CCF3 and (Me3Si)2(Ph2MeSi)CSiMe2Cl, respectively. |
