New computational and experimental evidence for the mechanism of the Sakurai reaction

Reaction of aldehydes with allyltrimethylsilane promoted by BF3, (Sakurai reaction) affords fluorotrimethylsilane and a borylated homoallylic alcohol in a noncatalytic fashion. These reaction products have been identified through C-13 NMR and Si-29 NMR. A model system formed by acetaldehyde, allylsilane, and BH2F has been used to investigate the mechanism of this reaction at the DFT computational level. Four transition states, quite close in energy, have been found for the model reaction. These transition states, which explain the stereochemical features of the Sakurai reaction, correspond to eight-membered cyclic structures deriving from C-C (tight) and Si-F (loosen) bond formation and synclynal (gauche) disposition of the reacting double bonds. No antiperiplanar or six-membered cyclic transition structures have been located.