[C:1]([O:7][C:8]1[CH:16]=[CH:15][C:14]([Br:17])=[C:13]([CH3:18])[C:9]=1[C:10]([OH:12])=O)(=[O:6])[C:2]([CH3:5])([CH3:4])[CH3:3].[CH3:19][O:20][C:21]1[CH:22]=[C:23]([CH3:31])[CH:24]=[C:25]([O:29][CH3:30])[C:26]=1[O:27][CH3:28].O=P12OP3(OP(OP(O3)(O1)=O)(=O)O2)=O>ClCCl>[Br:17][C:14]1[CH:15]=[CH:16][C:8]([O:7][C:1](=[O:6])[C:2]([CH3:3])([CH3:4])[CH3:5])=[C:9]([C:13]=1[CH3:18])[C:10]([C:22]1[C:23]([CH3:31])=[CH:24][C:25]([O:29][CH3:30])=[C:26]([O:27][CH3:28])[C:21]=1[O:20][CH3:19])=[O:12]A mixture of 50A (6.3 g, 20 mmol), 3,4,5-trimethoxytoluene (3.83 g; 21 mmol), P2O5 (12.0 g) and dichloromethane (100 ml) is stirred at room temperature for 16 hours. Subsequently, the dichloromethane is distilled off and the residue is diluted with water and ethyl acetate. The organic phase is washed with water and concentrated. The residue is purified by flash chromatography with petrol ethers/ethyl acetate (9:1 v/v) as eluent yielding the pure product as white crystals, 5.58 g, (58.2%).
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