[Na].[CH2:2]=[C:3]1[CH2:6][CH:5]([C:7](=[O:9])[CH3:8])[CH2:4]1.[O-]CC.[Na+].[C:14](OCC)(=[O:20])[C:15]([O:17][CH2:18][CH3:19])=[O:16]>CCO>[CH2:2]=[C:3]1[CH2:6][CH:5]([C:7](=[O:9])[CH2:8][C:14](=[O:20])[C:15]([O:17][CH2:18][CH3:19])=[O:16])[CH2:4]1Sodium (1.15 g, 49.9 mmol) was dissolved in dry EtOH (30 mL, denaturated with 5% diethylether). Compound 8a (5.5 g, 49.9 mmol, crude) was dissolved in dry EtOH (45 mL) and the above prepared sodium ethoxide solution was added. This mixture was stirred at rt for 15 min and then diethyl oxalate (6.8 mL, 49.9 mmol) was added dropwise. The reaction mixture was placed in a pre-heated (to 67° C.) oil bath and stirred at this temperature for 4.5 h. The mixture was left at rt overnight. The solvent was removed, EA (100 mL) and 1 M HCl (70 mL) were added and organic phase was separated. The aq. phase was re-extracted with EA (50 mL). The combined organic phases were washed with water, brine and dried over anh. Na2SO4. The solvent was removed under reduced pressure and the residue was purified on silica using hexanes/MTBE 9:1 as eluent giving pure product 8b. Yield: 6.29 g, 56% over two steps. 1H-NMR (CDCl3), δ (ppm): 6.36 (s, 1H), 4.85-4.80 (m, 2H), 4.34 (q, J=8.0 Hz, 2H), 3.35-3.25 (m, 1H), 3.05-2.85 (m, 4H), 1.36 (t, J=8.0 Hz, 3H).
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