1,2-Dicarbonyl compounds reacted with benzene in the presence of a strong acid, trifluoromethanesulfonic acid, to give gem-diphenylated ketones in high yields. The reaction was accelerated when the acidity of the medium was increased, supporting involvement of O,O-diprotonated 1,2-dicarbonyl species (i.e., 1,2-dihydroxyethylene dications) as the active electrophiles.