Practical Synthesis of Unsymmetrical Diarylacetylenes from Propiolic Acid and Two Different Aryl Bromides

Abstract

AbstractA palladium catalyst that mediates the one‐pot sequential Sonogashira and decarboxylative coupling of propiolic acid with two different aryl bromides has been developed. Selective coupling of the first aryl bromide was achieved in the presence of a copper‐free, monometallic catalyst generated in situ from allylpalladium chloride dimer and SPhos with tetra‐n‐butylammonium fluoride as the base in an N‐methyl‐2‐pyrrolidone/water solvent mixture. Upon addition of another aryl bromide and raising the temperature from 50 to 80 °C, the intermediate arylpropiolic acid underwent decarboxylative coupling to give the corresponding diarylacetylene. Thus, the new system permits a one‐pot three‐component synthesis of unsymmetrical diarylacetylenes from widely available aryl bromides, rather than expensive aryl iodides, and propiolic acid, rather than (trimethylsilyl)acetylene, as an inexpensive and easy‐to‐handle acetylene synthon. The process is highly selective, modular, and gives access to a wide range of unsymmetrical diarylacetylenes in good yields.