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

Abstract
The synthesis of 1-alkenylboronic acid pinacol esters via a palladium-catalyzed cross-coupling reaction of bis(pinacolato)diboron (pin2B2, pin = Me4C2O2) with 1-alkenyl halides or triflates was carried out in toluene at 50 °C in the presence of KOPh (1.5 equiv) and PdCl2(PPh3)2-2Ph3P (3 mol %). The borylation of acyclic and cyclic 1-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.