Synthesis of diaryl ethynes from calcium carbide

Abstract

The synthesis of diaryl ethynes from an inexpensive calcium carbide as acetylene surrogate via palladium catalyzed coupling reaction with aryl iodides was developed. A number of symmetrical diaryl ethynes were synthesized from various substituted aryl iodides including electron donating, electron withdrawing, heteroatoms, and labile functional groups. The reaction proceeded smoothly in mild conditions with commercially inexpensive reagents such as Pd(OAc)2, CuI and triethylamine in the presence of undried acetonitrile as solvent to generate the coupling products in good to high yields. Moreover, highly functionalized oligo(phenyleneethynylenes) were prepared in good yields demonstrating the high functional group compatibility of our methodology. The reaction mechanism was also investigated. The presence of water is required in order to drive the reaction completely suggesting the slow release of acetylene gas in the reaction condition from the hydrolysis of calcium carbide with water.