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A cobalt‐catalyzed annulation of o‐phenylenediamines and internal alkynes for the synthesis of quinoxalines is developed. This method provides a variety of quinoxalines in good to high yields under a simple and mild reaction conditions with molecular O2 as a terminal oxidant. Preliminary mechanistic studies show that a novel reaction mechanism is involved in the current reaction, which is different from the previous reported dicarbonyl compound mechanism via the oxidation of the alkyne. [ABSTRACT FROM AUTHOR]