The reaction of di(n-propyl)cyclopropenone ( 7), di(n-butyl)cyclopropenone ( 16), and bicyclo[12.1.0]pentadeca-1( 14)-en-7-yn-15-one (21) with CpCo(CO) 2 and CpCo(cod) yielded CpCo-complexed benzoquinone and cyclopentadienone derivatives. When 16 was reacted with CpCo(CO) 2 and a 10-fold surplus of 4-octyne, a mixture of CpCo-capped benzoquinone 25 and cyclopentadienone 26 was isolated. The reaction of cyclopropenone 16 containing a 13 C-labeled CO group with CpCo(CO) 2 yielded a CpCo-capped tetrakis(n-butyl)-p-benzoquinone with one 13 C nucleus per molecule as the main product. The mechanism of the formation of p-benzoquinone is discussed on the basis of the results of trapping and labeling experiments.