Palladium-catalyzed cross-coupling reaction of bis(pinacolato)diboron with 1-alkenyl halides or triflates: Convenient synthesis of unsymmetrical 1,3-dienes via the borylation-coupling sequence

The synthesis of 1-alkenylboronic acid pinacol esters via a palladium-catalyzed cross-coupling reaction of bis(pinacolato)diboron (pin(2)B(2), pin = Me4C2O2) with 1-alkenyl halides or triflates was carried out in toluene at 50 degreesC in the presence of KOPh (1.5 equiv) and PdCl2(PPh3)(2)-2Ph(3)P (3 mol %). The borylation of acyclic and cyclic I-alkenyl bromides and triflates was achieved in high yields with complete retention of configuration of the double bonds. The method was applied to the one-pot synthesis of unsymmetrical 1,3-dienes via the borylation-coupling sequence.