Potassium Hydroxide → 2,5-Diethynylthiophene

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To a 250 mL flask were added 2.5 g of 2,5-diiodothiophene (7.44 mmol), 100 mg of Cul, and 220 mg of Pd(Ph3P)2Cl2 under nitrogen. Then 100 mL of triethylamine (TEA) and 5.0 mL of trimethylsilylacetylene (3.40 g, 35 mmol) were injected. The reaction mixture was allowed to stir at room temperature for 12 hours. The precipitate was removed by filtration and the solvent of the filtrate was evaporated. The crude intermediate, i.e. 2,5-bis(trimethylsilylethynyl)thiophene, was purified by column chromatography and thus hydrolysed with 3 g KOH (53.6 mmol) in 70 mL methanol for 2 hours. The solution was poured into a large amount of water, and extracted with diethyl ether twice. The resultant solution was washed with water three times, dried over magnesium sulphate, and then the solvent was removed under reduced pressure to give 2,5-diethynylthiophene as a pale yellow liquid (0.71 g, 72%).

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