Synthesis of Unsymmetrical Aryl-Ethynylated Benzenes via Regiocontrolled Sonogashira Reaction of 1,3,5-Tribromobenzene

Sonogashira coupling of trimethylsilylacetylene with 4-alkyloxy-1-iodobenzenes gave 2-(4-(alkyloxy)phenyl)ethynyltrimethylsilanes which undergo deprotection via removal of TMS-group using tetrabutylammonium fluoride (TBAF) in THF at room temperature to afford the corresponding terminal 2-(4-(alkyloxy)phenyl)acetylenes. Regiocontrolled Sonogashira cross-coupling of 1,3,5-tribromobenzene with the terminal arylacetylenes in aqueous medium resulted in the formation of mono-, di- and tri-alkynylated benzene derivatives in moderate to good yields. Factors affecting the regioselective alkynylation were also examined.