Step 2; 4-(4-Chlorophenoxy)phenol; Following the general procedure of Example 12 (Step 2), boron tribromide (1.0 M dichloromethane solution, 9.66 mL, 9.66 mmol) was added to a solution of dichloromethane (15 mL) of the product of Step 1 (0.76 g, 3.22 mmol), and the reaction was completed to give 4-(4-chlorophenoxy)phenol ( 0.37 g, 52%), the product was a light green solid. Step 2; 4-(4-Chlorophenoxy)phenol; To a solution of dichloromethane (50 mL) of the product of Step 1 (2.86 g, 12.18 mmol) was added boron tribromide (1.0 M solution in dichloromethane, 30 mL, 30.5 mmol) dropwise over 5 min at -78 °C. The reaction mixture was stirred at -78°C for 1 hour, then warmed to ambient temperature and continued stirring for 1 hour. Upon completion of the reaction, the mixture was cooled to 0 °C and slowly added to cold water/dichloromethane (50 mL/50 mL). The organic phase was washed sequentially with water and brine, dried over anhydrous Na2SO4 and concentrated under reduced pressure. The crude product was purified by rapid chromatography on silica gel using hexane/EtOAc (gradient elution) to afford 4-(4-chlorophenoxy)phenol (2 g, 75%); 1H NMR (400 MHz, CDCl3) δ 4.8 (s, 1H), 7.23-7.26 (m, 2H), 6.81-6.92 (m, 6H). Step 2; 4-(4-Chlorophenoxy)phenol; Boron tribromide (7.6 mL, 80.3 mmol) was added dropwise over 5 min at -78 °C to a solution of dichloromethane (72 mL) of the product of step 1 (6.3 g, 26.8 mmol). The reaction mixture was stirred at -78 °C for 1 hour, then warmed to ambient temperature and continued stirring for 1 hour. Upon completion of the reaction, the mixture was cooled to 0 °C and slowly added to cold water/dichloromethane. The organic phase was washed sequentially with water and brine, dried over anhydrous Na2SO4 and concentrated under reduced pressure. The crude product was purified by rapid chromatography on silica gel using EtOAc/hexane (gradient elution) to afford 4-(4-chlorophenoxy)phenol (4.50 g, 76%).
