Oxidative Desilylation of Alkylsilanes with Triphenylcarbenium Ion. Control of Transition-State Geometry

Article abstract of DOI:10.1021/jo00317a009

Ten acylic, cyclic, and aralkyl-type silanes were treated with triphenylcarbenium tetrafluoroborate in dichloromethane to measure rates of oxidative desilylation: RCH2CH2SiR3+Ph3C(1+)BF4(1-)->Ph3CH+RCH=CH2+R3SiF+BF3.The divergence of rates, from Ph2CHCH2SiMe3, which was inert, through dimethylsilacyclopentane (k₂=4E-6), to dimethylsilacyclohexane (k₂=2.2E-3), can not be rationalized on purely electronic grounds.A transition state requiring anticoplanar arrangement of the silicon moiety and β-hydrogen to be extruded is proposed.Dimethylsilacyclobutane, which reacts extremely rapidly (k₂ approx. 2E-2), suffers allylic cleavage of the initially formed fluoro(2-propenyl)dimethylsilane.As the olefin products suffer decomposition or polymerization under the reaction conditions, this desilylation is of minimal preparative value.