[CH3:1][O:2][C:3]1[C:8]([O:9][CH3:10])=[C:7]([O:11][CH3:12])[CH:6]=[CH:5][C:4]=1[OH:13].[C:14]([O-])([O-])=O.[K+].[K+].CI.CCOC(C)=O>CC(C)=O>[CH3:12][O:11][C:7]1[CH:6]=[CH:5][C:4]([O:13][CH3:14])=[C:3]([O:2][CH3:1])[C:8]=1[O:9][CH3:10]Following the procedure by Tremblay et al.,17 17 (3.851 g, 20.9 mmol) was dissolved in dry acetone (90.0 ml), and K2CO3 (9.36 g, 67.7 mmol) was added followed by MeI (9.0 mL, 144 mmol). The reaction was heated under reflux for 26 h and monitored by TLC (1:9 EtOAc:hexanes) for completion. When complete the reaction was cooled to room temperature and filtered. The acetone was removed under reduced pressure and the residue was taken up in CH2Cl2 (50 mL). The suspension was filtered, dried over MgSO4, filtered again, and condensed. The crude product can be purified by flash chromatography (1:4 EtOAc:hexanes), however, recrystallization from Et2O/hexanes was sufficient to provide pure 18 (3.405 g, 17.2 mmol, 82%) as white needles.
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