Palladium-catalyzed double-bond migration of unsaturated hydrocarbons accelerated by tantalum chloride.

The operationally simple palladium-catalyzed double-bond migration without heteroatom-containing coordinating functional groups is described. Addition of TaCl5 as a second catalyst greatly enhanced the migration efficiency to provide β-alkylstyrenes through migration of up to a five-carbon chain. Both catalysts were commercially available, and the reaction occurred without external ligands under neutral conditions. The reaction proceeded via generation of π-allyl palladium species, which enabled the chemoselective double-bond migration of hydrocarbons in the presence of allylethers. Remote functionalization through double-bond migration was also demonstrated using FeCl3 as a second catalyst.