γ-Selective Cross-Coupling of Allylic Silanolate Salts with Aromatic Bromides Using Trialkylphosphonium Tetrafluoroborate Salts Prepared Directly from Phosphine•Borane Adducts

The gamma-selective, palladium-catalyzed cross-coupling of sodium (2)-2-butenyidiethylsilanolate with a variety of aromatic bromides Is reported. The protocol provides high yields (73-94%) and site selectivity (gamma/alpha, 25:1 -> >99:1) In the coupling of electron-rich, electron-poor, sterically hindered, and heteroaromatic bromides. The use of a configurationally homogeneous (Z)-slianolate, nontransferable ethyl groups, and a sterically bulky trialkylphosphonium tetrafluoroborate salt (t-BuCy(2)PH(+)BF(4)(-)) prepared directly from the corresponding air-stable phosphine center dot borane adduct are critical to the success of the method.