The [2+2+2+1] cycloaddition mechanism of enediynes and carbon monoxide catalyzed by the [Rh(CO)(2)Cl](2) rhodium dimer-has been studied using density functional theory, comparing this multistep process with the two-step reaction in the absence of a catalyst. According to our results, the multistep mechanism agrees with that previously suggested. The great selectivity of this reaction and the influence of the chosen solvent in this selectivity were also analyzed.