General procedure for the synthesis of 1,6-dibromo-2-naphthol from 6-bromo-2-naphthol: 6-bromo-2-naphthol (500 mg, 2.242 mmol, 1.0 eq.) was reacted with N-bromosuccinimide (NBS, 558.7 mg, 3.319 mmol, 1.4 eq.) in acetone (4.4 mL) and 1 N HCl (22 μL) in a mixed solution of acetone (4.4 mL) and 1 N HCl (22 μL) at room temperature with stirring for 15 min. Upon completion of the reaction, ethyl acetate was added for extraction and the organic phase was washed three times with 1 N HCl to remove unreacted NBS and by-products. Subsequently, the organic phase was dried with anhydrous magnesium sulfate, the desiccant was removed by filtration, and the filtrate was concentrated under reduced pressure on a rotary evaporator to afford the target product 1,6-dibromo-2-naphthol in quantitative yield (677 mg). The product characterization data were as follows: molecular formula C10H6Br2O; molecular weight 300/302/304; 1H NMR (CDCl3, δ): 7.90 (d, J = 1.8 Hz, 1H), 7.87 (d, J = 8.8 Hz, 1H), 7.61 (d, J = 8.8 Hz, 1H), 7.59 (dd, J = 2.1 Hz, J = 9.1 Hz, 1H), 7.24 (d, J = 8.8 Hz, 1H); 13C NMR (CDCl3, δ): 177.5, 151.0, 131.0, 130.6, 130.1, 128.4, 128.3, 127.2, 118.0, 106.1; IR (cm-1): 3443, 1688, 1617, 1586 1382, 1209, 1183, 1130.
