Cationic rearrangements controlled by the presence of a silyl group

1,1-Disilylcarbinols having two alkyl groups on the adjacent carbon atom react with thionyl chloride in sulfur dioxide to give the product in which one of the alkyl groups has migrated towards the two silyl groups, and one of the silyl groups has been removed from the resultant cation. The reaction is seen in ring-expansion, as in the conversion of cyclohexylbis[dimethyl(phenyl)silyl]carbinol (7) into 1-dimethyl(phenyl)silylcycloheptene (11), and in open chains, as in the conversion of 1,1-bis[dimethyl(phenyl)silyl]-2-methylpropanol (26) into (E)- and (Z)-2-dimethyl(phenyl)silylbut-2-ene (27). Phenyldimethylsilyllithium reacts with pinacolone to give the α-silyl carbinol (44), which rearranges in the same way to give 2,3-dimethylbut-2-ene (46), effectively achieving a pinacolone-to-pinacol rearrangement.