Density functional theory has been used to study an alternative mechanism for the ruthenium(II)-catalyzed [2 + 2 + 2] cycloaddition between 1,6-diynes and tricarbonyl compounds, proposing a multistep-pathway different from that which we previously reported. The dimerization mechanism to obtain the minority product of the reaction has also been studied in order to analyze the selectivity of this cycloaddition.