Palladium-Catalyzed Aerobic Synthesis of Terminal Acetals from Vinylarenes Assisted by [pi]-Acceptor Ligands

Terminal acetals were synthesized from various vinylarenes and 1,2- or 1,3-diols using a simple PdCl2(MeCN)2/methoxy-p-benzoquinone (MeOBQ)/CuCl catalyst system and 1atm of O2 under mild reaction conditions by the anti-Markovnikov nucleophilic attack of an oxygen nucleophile on the coordinated vinylarenes. Cyclic [alpha],[beta]-unsaturated carbonyl compounds such as MeOBQ and N-phenylmaleimide were especially effective as additives to afford higher yields of the desired terminal acetals. Kinetic experiments indicated that MeOBQ operates as a π-acceptor ligand for Pd to accelerate the reaction and that the dissociation of a chloride ion from Pd precedes the rate-determining step.