1,3-MIGRATION OF TRIORGANOSILYL GROUPS FROM CARBON TO OXYGEN IN HIGHLY CROWDED ORGANOSILANOLS

The silanol (Me3Si)CSiMe2OH has been shown to isomerize to (Me3Si)2CH(SiMe2OSiMe3) (which reacts further to give (Me3Si)2CH(SiMe2OMe)) in 0.5 M NaOMe/MeOH, the isomerization being ca. 90% complete after 6 h under reflux. Corresponding isomerizations of (PhMe2Si)3CSiMe2OH (to give (PhMe2Si)2CH(SiMe2OSiMe2Ph)), (Me3Si)2C(SiMePh2)SiMe2OH (to give (Me3Si)2CH(SiMe2OSiMePh2)), and (Me3Si)3CSiPh2OH (to give (Me3Si)2CH(SiPh2OSiMe3)) take place much more readily, and are complete within ca. 2 min at room temperature in 0.10 M NaOMe/MeOH. The reactions involve 1,3-migration from carbon to oxygen within a silanolate ion to give a carbanion, which rapidly acquires a proton from the solvent. The migration is facilitated by relief of steric strain and stabilization of the forming carbanionic centre by the three attached silyl groups. The relative reactivities of the various silanols may be determined by the magnitude of the release of steric strain, by the inherent ease of nucleophilic attack at the relevant silicon centre, and, at least at low base concentrations, by the acidity of the silanol. Treatment of (Me3Si)3CSiPh2OH with MeLi in Et2O/THF gives, by the same rearrangement, the organolithium reagent (Me3Si)2CLi(SiPh2OSiMe3), which on treatment with Me2SiHCl gives (Me3Si)2C(SiMe2H)(SiPh2OSiMe3). © 1990.