Novel anti-Markovnikov regioselectivity in the Wacker reaction of styrenes

The Wacker reaction is one of the longest known palladium-catalysed organic transformations, and in the vast majority of cases proceeds with Markovnikov regioselectivity. Palladium(II)-mediated oxidation of styrenes was examined and in the absence of reoxidants was found to proceed in an anti-Markovnikov sense, giving aldehydes. Studies on the mechanism of this unusual transformation were carried out, and indicate the possible involvement of a η4-palladium–styrene complex. With a heteropolyacid as the terminal oxidant, oxidation of styrene to give the anti-Markovnikov aldehyde as the major product was found to be catalytic.