I[C:2]1[CH:7]=[CH:6][C:5]([S:8]([N:11]2[CH2:16][CH2:15][O:14][CH2:13][CH2:12]2)(=[O:10])=[O:9])=[CH:4][CH:3]=1.[B:17](OC(C)C)([O:22]C(C)C)[O:18]C(C)C.[Li]CCCC.Cl>C1COCC1.CCCCCC>[N:11]1([S:8]([C:5]2[CH:6]=[CH:7][C:2]([B:17]([OH:22])[OH:18])=[CH:3][CH:4]=2)(=[O:10])=[O:9])[CH2:16][CH2:15][O:14][CH2:13][CH2:12]1
To a solution of 25 g of the compound obtained in Step A (70.8 mmol) and 26 ml of triisopropyl borate in 400 ml of THF cooled to −60° C. there are added, dropwise, over 45 minutes and under a gentle current of nitrogen, 53 ml of a 1.6M solution of BuLi (84.9 mmol) in hexane. The reaction solution is then stirred for 1 hour 30 minutes at −60° C. and is subsequently returned to ambient temperature over 2 hours. The reaction mixture is treated with about 100 ml of 1N HCl and is extracted 3 times with ethyl acetate. The organic phases are collected, washed with brine, dried (MgSO4) and evaporated under reduced pressure. The residue obtained is chromatographed on an SiO2 column, eluting with CH2Cl2 and then with a mixture of CH2Cl2/MeOH 98/2 and then 95/5. After evaporation of the fractions, the residue is triturated in ethyl ether to yield the title product after filtration.
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