Synthesis of 1,3,5-Tris[(4′-ethynylphenyl)ethynyl]benzene

Several synthetic routes were designed to prepare 1,3,5-tris[(4-ethynylphenyl)ethynyl]benzene. The synthetic routes and reaction conditions were contrasted and discussed, when multiple Sonogashira reactions were occurred between multifunctional alkyne-terminal compounds and aromatic bromine compounds, the different substitution degree compounds with similar polarity were obtained, and they were difficult to separate. Whereas the reactions between multifunctional alkyne-terminal compounds and aromatic iodine compounds can avoid this situation. 1,3,5-Tribromobenzene reacted with 3-methylbutynol to afford 1,3,5-tris(3'-hydroxy-3'-methyl-but-1'-ynyl)benzene, then 1,3,5-triethynylbenzene was obtained by the cleavage reaction of the compound in presence of potassium hydroxide and toluene. On the other hand, using 4-iodoaniline and trimethyl silyl acetylene as raw materials, 4-trimethylsiylethynyl iodobenzene was synthesized by diazo reaction and halogenation. Therefore, 1,3,5-tris[(4'-ethynylphenyl)ethynyl]benzene was prepared by the cleavage reaction of the 1,3,5-triethynylbenzene and 4-trimethylsiylethynyl iodobenzene. The structures of the target compound and intermediates were confirmed by H-1 NMR, C-13 NMR techniques and element analysis.