In a 5 mL microwave reaction vial, the vial was purged with argon for 15 min to remove oxygen. Cetyltrimethylammonium bromide (CTAB, 219 mg, 0.6 mmol), potassium carbonate (K2CO3, 278 mg, 2 mmol), 3-thiopheneboronic acid (256 mg, 2 mmol) and palladium catalyst (0.025 mmol) were added. The vial was again purged with argon for 5 min, followed by the addition of 4 mL of degassed water. 4-Bromopyridine hydrochloride (158 mg, 1 mmol) was added and sodium hydroxide (powder, 44 mg, 1.1 mmol) was added to neutralize the hydrochloride and release the free base form of 4-bromopyridine. Note: The use of only one equivalent of potassium carbonate is not sufficient to react 4-bromopyridine hydrochloride effectively. The mixture is stirred and sonicated to obtain a homogeneous solution, which is then reacted in a preheated oil bath for 24 hours or in a microwave reactor at the appropriate temperature for 30 minutes. After completion of the reaction, the reaction mixture was diluted with 5 mL of water and extracted with ethyl acetate (35 mL). To compare the extraction efficiency, dichloromethane (5 × 5 mL), ether (2-3 × 5 mL) and ethyl acetate (2-3 × 5 mL) were also tested, which showed comparable extraction efficiencies for these solvents. The organic layers were combined, dried with anhydrous sodium sulfate and concentrated in vacuum. The crude product was purified by fast chromatography to afford the target product 4-(thiophen-3-yl)pyridine. The yield was calculated based on the starting 4-bromopyridine hydrochloride.
