Ionic Liquid-Promoted Regioselective Catalysis by Palladium

The palladium catalyzed Heck arylation of several electron-rich olefins, has been accomplished in the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF4], using as the arylating agents aryl bromides instead of the commonly used, but commercially unavailable and expensive aryl triflates. The reaction proceeded with high efficiency and remarkable regioselectivity without the need for costly or toxic halide scavengers, leading exclusively to branched products. The unique regiocontrol appears to stem from the ionic environment provided by the ionic liquid, which alters the reaction pathway in such a way that the ionic mechanism is made favorable. The method is simple and highly effective and contributes to the extension of Heck reaction to a wider range of substrates.