Palladium-catalyzed regioselective hydroboration of aryl alkenes with B2pin2

A palladium(II)-catalyzed hydroboration of aryl alkenes with stable and easy-to-handle (pinacolato) diboron (B(2)pin(2)) under mild conditions has been developed. Acetic acid acted as the solvent and the hydrogen source, which has been identified by deuterium experiments. Notably, isomerization-hydroboration of allyl benzene derivatives was observed. As a result, a series of benzyl boronic esters were obtained in moderate to excellent yields with exclusive regioselectivity.