Diphenylphosphine and 1,2-dichlorohexafluorocyclobutene react in a solvent medium of dimethyl formamide to give both the mono (3) and 1,2-disubstituted (2) derivatives as products. In contrast, these same reactants give entirely different products when the reaction is conducted in the absence of a solvent.Analytical and spectroscopic data are presented for the proposed structures.