Step (b) 3-bromo-4-methoxyphenylacetic acid (14.0 g, 0.057 mol) and anhydrous dichloromethane (100 mL) were added to a 250 mL round bottom flask. The reaction mixture was degassed by nitrogen bubbling for 5 min. Subsequently, a dichloromethane solution of 1 M boron tribromide (63 mL, 0.063 mol) was added slowly and dropwise through the addition funnel. The reaction mixture was stirred at room temperature and a white solid was observed to precipitate gradually. After the reaction was carried out for 2 h, the product was separated by filtration and the collected white crystals were washed several times with dichloromethane to finally obtain 3-bromo-4-hydroxyphenylacetic acid (12 g, 92% yield).
