Stereo- and Regioselectivity of Reactions of Siliranes with Aldehydes and Related Substrates

Siliranes undergo stereoselective and regioselective insertions of benzaldehyde to provide oxasilacyclopentane products. The thermal reaction (>100°C) leads to more decomposition and side products, whereas the catalyzed variant (t-BuOK, <25°C) proceeds more cleanly with a high degree of inversion (>95%). Treatment of siliranes with enolizable aldehydes leads to silyl enol ethers. The reaction of a silirane at high temperatures with an imine leads to reductive dimerization, presumably by way of intermediate-free silylene. The mechanism for the catalyzed insertion of benzaldehyde is discussed.