A palladium(II)-catalyzed hydroboration of aryl alkenes with stable and easy-to-handle (pinacolato)diboron (B₂pin₂) 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.