Palladium-catalyzed reactions of aryl iodides with trimethylsilylacetylenes and disubstituted alkynes: the synthesis of diarylacetylenes and triarylethylenes

Treatment of 2.5 equiv. of aryl iodide with trimethylsilylacetylene in the presence of 3 equiv. of sodium methoxide and 5 mol% of Pd(PPh3)4 under refluxing methanol for 6 h gave diarylacetylene in good chemical yields. When the catalyst was replaced by Pd(dba)2 and 5 equiv. of aryl iodide were added under the same reaction conditions, triarylethylenes were obtained in 70–85% yields. Only the sterically hindered o-methoxyiodobenzene and 2-iodothiophene gave the diarylacetylene, but also in good chemical yield. Reaction of aryl iodides with disubstituted alkynes in the presence of Pd(OAc)2 and sodium methoxide in methanol produced trisubstituted ethylenes in modest to good yields. The hydrogenolysis of the organopalladium is proposed through β-hydride elimination of the palladium methanolate intermediates.