Boron trifluoride etherate → 6-Methoxy-1-benzothiophene

Boron trifluoride etherate (8.15 mL) dissolved in dry dichloromethane (407 mL) was stirred rapidly at 0° C. under nitrogen and a solution of (3-methoxyphenylsulphanyl)acetaldehyde (11.5 g, 63.10 mmol) in dry dichloromethane (29 mL) was added dropwise over 25 min. The resultant green solution was stirred for 2 min and then saturated aqueous sodium bicarbonate solution (150 mL) was added at a rate so as to maintain the temperature <8° C. The reaction mixture was stirred for 5 min and then the layers were separated and the organic layer was washed with saturated aqueous sodium bicarbonate solution (100 mL) and water (100 mL). The organic phase was dried (MgSO4), and concentrated in vacuo. The product was purified by distillation to afford the title compound as a colourless oil (6.29 g, 61%, b.p. 83-88° C. at 16 mBar).