[CH2:1]([O:8][C@H:9]([CH3:14])[C@H:10]([OH:13])[CH2:11][OH:12])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.O.[C:16]1(C)[CH:21]=CC(S(O)(=O)=O)=C[CH:17]=1.COC(OC)(C)C.S([O-])([O-])(=O)=O.[Na+].[Na+]>C1(C)C=CC=CC=1.CCOC(C)=O.C(=O)(O)[O-].[Na+]>[CH2:1]([O:8][C@@H:9]([C@H:10]1[CH2:11][O:12][C:16]([CH3:21])([CH3:17])[O:13]1)[CH3:14])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1
A stirred solution of (2R,3R)-3-(benzyloxy)butane-1,2-diol (the product of step ii) (0.68 g), p-toluene sulfonic acid monohydrate (34 mg) and 2,2-dimethoxypropane (0.43 mL) in toluene (10 mL) was heated to reflux for 30 min, then anhydrous sodium sulfate was added and reflux continued for 2.5 h. The reaction mixture was allowed to cool and diluted with EtOAc and saturated aqueous sodium bicarbonate and the layers separated. The organic extract was washed with brine, dried (MgSO4), filtered and evaporated. The residue was purified by column chromatography on silica gel using EtOAc/isohexane (1:9 to 1:1 gradient) as eluent to give the subtitle compound as a colourless liquid. Yield: 0.46 g.
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