A mild, palladium-catalyzed method for the dehydrohalogenation of alkyl bromides: Synthetic and mechanistic studies

We have exploited a typically undesired elementary step in crosscoupling reactions, <i>β</i>-hydride elimination, to accomplish palladium-catalyzed dehydrohalogenations of alkyl bromides to form terminal olefins. We have applied this method, which proceeds in excellent yield at room temperature in the presence of a variety of functional groups, to a formal total synthesis of (R)-mevalonolactone. Our mechanistic studies have established that the rate-determining step can vary with the structure of the alkyl bromide and, most significantly, that L₂PdHBr (L = phosphine), an intermediate that is often invoked in palladium-catalyzed processes such as the Heck reaction, is <i>not</i> an intermediate in the active catalytic cycle.