C[O:2][C:3]1[CH:4]=[CH:5][C:6]2[O:11][CH2:10][CH2:9][N:8]([CH2:12][CH2:13][NH:14][C:15](=[O:17])[CH3:16])[C:7]=2[CH:18]=1.B(Br)(Br)Br.C(=O)([O-])O.[Na+]>ClCCl>[OH:2][C:3]1[CH:4]=[CH:5][C:6]2[O:11][CH2:10][CH2:9][N:8]([CH2:12][CH2:13][NH:14][C:15](=[O:17])[CH3:16])[C:7]=2[CH:18]=1Under argon, the compound obtained in Example 1 (342 mg; 1.37 mmol) is dissolved in 8 ml of distilled dichloromethane. The solution is cooled to −78° C., and then boron tribromide (4 eq.; 5.47 mmol; 5.17 μl) diluted with 5 ml of dichloromethane is slowly added. The mixture is left for one hour at −78° C. and then for 2 hours at ambient temperature. The reaction mixture is hydrolysed to pH 7 with a saturated sodium hydrogen carbonate solution and then the aqueous phase is extracted 4 times with dichloromethane. The organic phases are combined, and then removed under reduced pressure. The solid obtained is dissolved in a minimum amount of dichloromethane, precipitated in the presence of pentane, filtered, and then washed with an Et2O/pentane mixture.
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