Ruthenium(II)-catalyzed C-H functionalization of N-arylhydantoins is herein described. The biologically relevant hydantoin (imidazolidinedione) heterocycle functions as a weakly coordinating directing group in a C-H alkenylation reaction. The reaction gave a wide scope of 23 examples with yields up to 94% in the green solvent 2-MeTHF. Functionalization of API nilutamide (antiandrogen) is also reported. The use of the succinimide heterocycle as a directing group is also demonstrated in modest yields.