One‐Pot Synthesis of Unsymmetrical 1,3‐Butadiyne Derivatives and their Application in the Synthesis of Unsymmetrical 2,5‐Diarylthiophenes

A one‐pot protocol was developed for the synthesis of unsymmetrical 1,3‐butadiynes. The procedure is based on two sequential reactions: deprotection of R–C≡C–C≡C–C(Me)2OH derivatives in a retro‐Favorskii reaction to furnish a terminal 1,3‐butadiyne compound, which reacted with aryl iodides in a Sonogashira‐type cross‐coupling reaction catalyzed by Pd(PPh3)4 and CuI, using TBAOH as activator and toluene as solvent under reflux for 10 min. We also studied in situ thiocyclization of 1,3‐butadiynes, leading to unsymmetrical 2,5‐diarylthiophenes. The principal features of this method are operational simplicity, good substrate scope, very fast reaction, and high yields. A one‐pot, fast, and efficient protocol was developed to synthesize unsymmetrical 1,3‐diynes, consisting of a retro‐Favorskii reaction to furnish a terminal diacetylenic compound, and its coupling with organic iodide in a Sonogashira reaction under reflux in toluene for ten minutes. The described protocol was also extended to prepare 2,5‐diarylthiophenes through in situ thiocyclization of 1,3‐butadiynes.