Mechanistic studies of the palladium-catalyzed ring opening of oxabicyclicalkenes with dialkylzinc

The mechanism of the palladium-catalyzed ring opening of oxabicyclic alkene s with dialkylzinc has been studied, Experiments which rule out a pi -allyl mechanism were carried out. Trapping carbometalated products and synthesis and successful reaction of alkyl palladium species provided strong evidenc e in favor of an enantioselective carbopalladation as the key step in the m echanism. The studies also suggest that a cationic palladium species is res ponsible for carbopalladation of the alkene. The combination of palladium a nd dialkylzinc is unique in that the dialkylzinc functions both in the tran smetalation to palladium and as a Lewis acid in forming the reactive cation ic palladium species.