Oxidation of unsymmetrical diarylacetylenes ArC≡CAr′ in the CF₃COOH-CH₂Cl₂-PbO₂ system at 0-2°C in 1-3 h yields either pure 1,2,3,4-tetraaryl-2-butene-1,4-diones or mixtures of three isomeric γ-di-ketones Ar(Ar′CO)C=C(COAr′)Ar, Ar′(ArCO)C=C(COAr)Ar′, and Ar′(ArCO)C=C(COAr′)Ar which are predominantly Z isomers. The effect of electronic properties of the substituents in diarylacetylenes on the regio- and stereoselectivity of the reaction is discussed.