[Sn](Cl)(Cl)(Cl)Cl.[CH2:6]([O:9][C:10]1[CH:16]=[CH:15][CH:14]=[C:12]([OH:13])[C:11]=1[OH:17])[CH:7]=[CH2:8].[C:18]([O-])(O)=[O:19].[Na+].C(O)(=O)CC(CC(O)=O)(C(O)=O)O>C(Cl)Cl>[CH2:6]([O:9][C:10]1[CH:16]=[CH:15][C:14]([CH:18]=[O:19])=[C:12]([OH:13])[C:11]=1[OH:17])[CH:7]=[CH2:8]Tin tetrachloride (0.31 g, 0.14 mL, 1.32 mmol) was added to a solution of 39 (0.20 g, 1.20 mmol) and αα′-dichloromethyl methyl ether (0.15 g, 0.12 mL, 1.32 mmol) in CH2Cl2 at −78° C. The pale brown reaction mixture was stirred at this temperature for 1.5 h, then poured into an excess of saturated NaHCO3 aq. cooled at 0° C. The mixture was stirred for 15 min, acidified to pH 5 by the addition of 5% w/v citric acid then extracted with CH2Cl2 (3×). The organic phase was dried (Na2SO4) and evaporated to dryness to give 40 compound (0.18 g, 76%) which was used as such in the next step.
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