Theoretical study of thermal rearrangements of alpha-silylalcohols: Effects of substituents attached to the silicon atom on the reactions

To investigate the effects of substituents attached to the silicon atom on the thermal rearrangement reactions of alpha-silyl alcohols, the thermal rearrangement reactions of dimethylsilyl methanol (CH3)(2)SiHCH2OH and vinylsilyl methanol CH2=CHSiH2CH2OH were studied by ab initio calculations at the G3 level. Geometries of various stationary points were fully optimized at the MP2(full)/6-31G(d) and MP2(full)/6-311G(d,p) levels, and harmonic vibrational frequencies were calculated at the same levels. The reaction paths were investigated and confirmed by intrinsic reaction coordinate (IRC) calculations at the MP2(full)/6-31G(d) level. The results show that two dyotropic reactions could occur when (CH3)(2)SiHCH2OH or CH2=CHSiH2CH2OH is heated. One is Brook rearrangement reaction (reaction A), and the dimethylsilyl or vinylsilyl groups migrates from carbon atom to oxygen atom coupled with a simultaneous migration of a hydrogen atom from oxygen atom to carbon atom passing through a double three-membered ring transition state, forming dimethylmethoxylsilane (CH3)(2)SiHOCH3 or methoxylvinylsilane CH2=CHSiH2OCH3; the other is a hydroxyl group migration (reaction B) from carbon atom to silicon atom, coupled with a simultaneous migration of a hydrogen atom from silicon atom to carbon atom, via a double three-membered ring transition state, forming trimethylsilanol (CH3)(3)SiOH or methylvinylsilanol CH3SiH(OH)CH=CH2. The G3 barriers of the