A catalytic system combined with NiBr2 and diphenylphosphine oxide that enabled direct access to the valuable arylacetic acids from inexpensive alkylarenes and H2O via oxidative carbonylation was developed. Alkylarenes with primary and secondary benzylic C-H bonds were compatible with this method. Remarkably, the marketed drugs ibuprofen and diclofenac could be easily obtained by this procedure straightforwardly.