Oxidative Phosphonylation of Aromatics with Ammonium Cerium(IV) Nitrate Arylphosphonates 5 and 6 can be prepared in good yields in a one-step synthesis starting from arenes with tri- or diethylphosphites and cerium ammonium nitrate (CAN) as oxidant. The selectivity of the oxidative phosphonylation is relatively low; the reactive species is a phosphite radical cation.