AbstractCycloocteno‐1,2,3‐selenadiazole (1) and cyclopenta‐dienyldicarbonylcobalt (2) react in the presence of an excess of elemental sulfur to yield the dithiolene cyclopentadienyl(1,2‐cyclooctenedithiolato)cobalt (3). Available evidence indicates that this reaction involves the intermediacy of a cobalt–alkyne complex. Compound 3 is the first example of a cyclopentadienylcobalt dithiolene bearing aliphatic substituents. Analogous reactions performed using only catalytic quantities of 2 provide high‐yield syntheses of bis(cycloocteno)‐1,4‐dithiin (6) and bis(cycloocteno)‐1,4‐diselenin (7), whose structures have been determined by X‐ray diffraction.