γ-Selective cross-coupling of allylic silanolate salts with aromatic bromides using trialkylphosphonium tetrafluoroborate salts prepared directly from phosphine•borane adducts

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