Abstract
Details of a study on the intramolecular bis-silylation of C-C multiple bonds promoted by a new catalyst system, palladium-tert-alkyl isocyanide, are described. With a disilanyl ether derived from a homoallylic alcohol, intramolecular regioselective addition of the Si-Si linkage to the C=C bond took place to furnish an exo-ring closure product, i.e., 1, 2-oxasilolane. The bis-silylation of alkenes having substituents α to the C=C bond gave trans-3, 4-disubstituted oxasilolanes, while substitution β to the C=C bond favored cis-3, 5-disubstituted oxasilolanes. The 1, 2-oxasilolanes thus produced stereoselectively were oxidatively converted to the corresponding 1, 2, 4-triols. The present methodology for the synthesis of 1, 2, 4-triols was successfully extended to the stereoselective synthesis of 1, 2, 4, 5, 7- and 1, 2, 4, 6, 7-pentaols through a sequence of the intramolecular bis-silylation. The bis-silylation was also performed with alkenes linked to disilanyl groups through a 3-carbon chain and through an amide linkage. Alkenes tethered to disilanyl groups through chains of 2 atoms underwent similar intramolecular bis-silylation. The intramolecular bis-silylation of an alkyne tethered to a disilanyl group furnished a bis-silylated exocyclic olefin. Subsequent hydrogenation from the less-hindered side of the ring produced cis-disubstituted oxasilolane, providing an alternative method for the stereoselective synthesis of 1, 2, 4-triols. The intramolecular bis-silylation under high pressure led to the efficient synthesis of a new cyclic tetrakis(organosilyl)ethene, which possessed a non-twisted structure.
