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 re fluxing 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 a dded under the same reaction conditions, triarylethylenes were obtained in 70-85% yields. Only the sterically hindered o-methoxyiodobenzene and 2-iodo thiophene gave the diarylacetylene, but also in good chemical yield. Reacti on of aryl iodides with disubstituted alkynes in the presence of Pd(OAc)(2) , and sodium methoxide in methanol produced trisubstituted ethylenes in mod est to good yields. The hydrogenolysis of the organopalladium is proposed t hrough P-hydride elimination of the palladium methanolate intermediates. (C ) 2001 Elsevier Science Ltd. All rights reserved.