DFT-Based Explanation of the Effect of Simple Anionic Ligands on the Regioselectivity of the Heck Arylation of Acrolein Acetals

The Heck arylation of acrolein acetal has been studied computationally and compared to the corresponding reaction with allyl ethers. The reaction can be controlled to give either cinnamaldehydes or arylpropanoic esters by addition of different coordinating anions, acetate, or chloride. The computational study reveals that coordinating acetate raises the energy of an intermediate sufficiently to block the access to an otherwise favorable beta-hydride elimination. The reaction path is also compared to that of allyl ethers, which always give significant amounts of cinnamyl ether products under all reaction conditions. The difference between the two substrate classes could be rationalized in terms of relative hydride donating power of the two substrates.