C(N(CC)CC)C.[OH:8][CH2:9][CH:10]([CH:26]([CH3:28])[CH3:27])[CH2:11][CH:12]1[CH2:16][O:15][C:14]([CH3:18])([CH3:17])[N:13]1[C:19]([O:21][C:22]([CH3:25])([CH3:24])[CH3:23])=[O:20].S(=O)(=O)(O)[O-].[K+]>CS(C)=O.ClCCl>[CH:9]([CH:10]([CH:26]([CH3:28])[CH3:27])[CH2:11][CH:12]1[CH2:16][O:15][C:14]([CH3:18])([CH3:17])[N:13]1[C:19]([O:21][C:22]([CH3:25])([CH3:24])[CH3:23])=[O:20])=[O:8]6.97 ml of triethylamine are added dropwise at 0° C. to the solution of 3.0 g of tert-butyl 4-(2-hydroxymethyl-3-methylbutyl)-2,2-dimethyloxazolidine-3-carboxylate in 11 ml of dimethyl sulphoxide and 55 ml of dichloromethane. 5.23 g of sulphur trioxide-pyridine complex are added in 3 portions at intervals of 10 minutes and the reaction mixture is stirred at 0° C. for a further 3 hours. The reaction mixture is poured onto ice-water, adjusted to pH=2.5 with saturated aqueous potassium bisulphate solution and extracted with diethyl ether (3×)—the combined organic phases are washed successively with water and 5% aqueous sodium hydrogencarbonate solution, dried over sodium sulphate and concentrated by evaporation. The title compound is obtained from the residue as a yellow oil. Rf=0.46 (1:2 EtOAc-heptane).
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