Cobalt(III)-catalyzed C–H amidation of arenes has been realized under assistance of weakly coordinating carbonyl groups with 1,4,2-dioxazol-5-ones as the amidating reagents. Both sulfoxonium ylides and α-benzoylketene dithioacetals are viable arene substrates. The coupling system features high yield, broad substrate scope, and functional group tolerance, providing a series of functionalized sulfur-containing compounds.