C[O:2][C:3]1[CH:22]=[CH:21][CH:20]=[C:19]([O:23]C)[C:4]=1[O:5][CH2:6][C@H:7]([O:14][S:15]([CH3:18])(=[O:17])=[O:16])[CH2:8][O:9][S:10]([CH3:13])(=[O:12])=[O:11].B(Br)(Br)Br.O>ClCCl>[OH:23][C:19]1[CH:20]=[CH:21][CH:22]=[C:3]([OH:2])[C:4]=1[O:5][CH2:6][C@H:7]([O:14][S:15]([CH3:18])(=[O:16])=[O:17])[CH2:8][O:9][S:10]([CH3:13])(=[O:11])=[O:12]Methanesulfonic acid (S)-3-(2,6-dimethoxy-phenoxy)-2-methanesulfonyloxy-propyl ester (3.08 g, 8.00 mmol) in) in dichloromethane (40 ml) was cooled to 0° C. and stirred under nitrogen atmosphere. Boron tribromide (1 M solution in dichloromethane, 18 ml, 18 mmol) was added in 15 min. The mixture was stirred at +25° C. for 4 h, and poured on mixture of ice (10 g) and water (15 ml), and the layers were separated. Organic phase was recovered and water layer was extracted twice with dichloromethane (15 ml). Organic phase and dichloromethane extracts were combined and washed with water (15 ml) and saturated sodium chloride solution (15 ml). The combined organic phase was dried (Na2SO4), filtered and evaporated to dryness to give 2.53 g of the title compound.
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