General procedure for the synthesis of (S)-6,6'-dibromo-1,1'-bi-2-naphthol from (S)-1,1'-bi-2-naphthol: (S)-BINOL (7.20 g, 25.0 mmol, 1.0 eq.) was suspended in dichloromethane (250 mL) at -78 °C. A solution of bromine (3.9 mL, 34.0 mmol, 1.4 eq.) in dichloromethane (40 mL) was added slowly dropwise to the reaction mixture (dropwise time 20-30 min) and stirring was continued at -78 °C for 15 min. The reaction mixture was allowed to warm up slowly to room temperature and the progress of the reaction was monitored by thin layer chromatography (TLC) (about 3 hours) until the reaction was complete. The reaction was quenched by the addition of saturated aqueous sodium thiosulfate (50 mL) and the aqueous layer was extracted with ethyl acetate (3 x 50 mL). The organic layers were combined, dried with anhydrous magnesium sulfate, filtered and concentrated under reduced pressure to remove the solvent. The product was recrystallized by dichloromethane/pentane to afford (S)-6,6'-dibromo-1,1'-bian-2-naphthol as a white solid (10.34 g, 23.3 mmol, 93% yield).1H NMR (300 MHz, CDCl3) δ: 8.03 (d, J = 1.9 Hz, 2H), 7.87 (d, J = 9.0 Hz, 2H), 7.45-7.35 (m, 4H), 6.94 (d, J = 9.0 Hz, 2H), 5.00 (bs, 2H). 13C NMR (75 MHz, CDCl3) δ: 153.0, 131.9, 130.8, 130.7, 130.6, 130.4, 125.9, 119.0, 118.0, 110.7. The analytical data are in agreement with the literature.
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