Tandem Pd-catalyzed double C-C bond formation: effect of water.

A highly efficient water-accelerated palladium-catalyzed reaction of gem-dibromoolefins with a boronic acid via a tandem Suzuki-Miyaura coupling and direct arylation is reported. A wide range of aryl, alkenyl, and alkyl boronic acids, as well as a variety of substitution patterns on the phenyl ring, are tolerated. Additionally, mechanistic studies were conducted to ascertain the order of the couplings as well as the role(s) of water. Results from this study indicate that the major pathway is a Suzuki-Miyaura coupling/direct arylation sequence and that water accelerates the Pd(0) formation and Suzuki-Miyaura coupling.