[C:1](=O)([O-])[O-].[K+].[K+].[CH2:7]([O:9][CH2:10][O:11][C:12]1[CH:17]=[C:16]([O:18][CH2:19][O:20][CH2:21][CH3:22])[CH:15]=[CH:14][C:13]=1[OH:23])[CH3:8].CI>CN(C)C=O>[CH2:7]([O:9][CH2:10][O:11][C:12]1[CH:17]=[C:16]([O:18][CH2:19][O:20][CH2:21][CH3:22])[CH:15]=[CH:14][C:13]=1[O:23][CH3:1])[CH3:8]Potassium carbonate (14.3 g, 103 mmol) was added to 3a (2.50 g, 10.3 mmol) in N,N-dimethylformamide (103 mL). After 10 minutes, methyl iodide (6.43 mL, 103 mmol) was added and the solution was heated to reflux for 12 hours. Upon cooling to room temperature, the solution was extracted with EtOAc (3×50 mL); combined organic fractions were washed with saturated aqueous NaCl, dried (Na2SO4), and concentrated. The residue was purified by column chromatography (SiO2, 4:1 Hexane:EtOAc) to afford 4a as a yellow oil (2.40 g, 91%): 1H NMR (CDCl3, 500 MHz) δ 6.87 (d, J=2.8 Hz, 1H), 6.72 (d, J=8.9 Hz, 1H), 6.60 (dd, J=13.3, 1.7 Hz, 1H), 5.18 (s, 2H), 5.07 (s, 2H), 3.76 (s, 3H), 3.72-3.69 (m, 2H), 3.68-3.63 (m, 2H), 1.17-1.13 (m, 6H); 13C NMR (CDCl3, 125 MHz) δ 150.7, 146.2, 143.9, 111.2, 107.9, 105.8, 93.2, 93.0, 63.3, 63.0, 55.4, 14.1, 14.0; IR (film) νmax 2976, 2932, 2899, 2835, 1595, 1508, 1393, 1227, 1153, 1103, 1080, 1009, 847 cm−1; HRMS (ESI+) m/z: [M+Na]+ calcd for C13H20O5, 279.1208. found, 279.1181.
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