Pd-Catalyzed Heck Reactions of Aryl Bromides with 1,2-Diarylethenes

A catalytic system composed of Pd(OAc)(2) and P(o-tol)(3) was found to be effective for the Heck reaction of aryl bromides with diarylethylenes. Using K(2)CO(3) as a base and DMF as a solvent, trisubstituted olefins were obtained in good to excellent yields. Aryl bromides containing an electron-withdrawing group in para position were less reactive for the Heck coupling reaction and gave substantial amount of homocoupling by-product suggesting that oxidative addition is not the rate-determining step. Electron withdrawing group substituent in the para position of stilbene affects the regioselectivity of the reaction. In this case, the phenyl group from the Ph-Pd complex migrates preferentially to the same carbon of the double bond to which the phenyl is bonded. Finally, a one pot sequential double Heck arylation of styrene was performed, giving trisubstituted olefin with an overall yield of 73%.