[CH3:1][C:2]1[C@H:8]2[C@H:5]([CH2:6][C:7]2=O)[CH2:4][CH:3]=1.[H-].[Na+].COP([CH2:18][C:19]([O:21][C:22]([CH3:25])([CH3:24])[CH3:23])=[O:20])(OC)=O>O1CCCC1>[CH3:1][C:2]1[C@H:8]2[C@H:5]([CH2:6][C:7]2=[CH:18][C:19]([O:21][C:22]([CH3:25])([CH3:24])[CH3:23])=[O:20])[CH2:4][CH:3]=1(±)-(1S,5R)-4-methylbicyclo[3.2.0]hept-3-en-6-one (1.10 g, 9.0 mmol) was added to a reaction solution prepared in advance by adding sodium hydride (>65% oil, 342.8 mg, 9.0 mmol) to a tetrahydrofuran solution (10 mL) of tert-butyl dimethoxyphosphorylacetate (2.08 g, 9.3 mmol) under ice cooling, and the mixture was further stirred for 2 hours. The reaction solution was separated into aqueous and organic layers by the addition of a saturated aqueous solution of ammonium chloride and saturated saline. The aqueous layer was subjected to extraction with ethyl acetate. These organic layers were combined, then washed with saturated saline, and then dried over anhydrous magnesium sulfate. The solvent was distilled off under reduced pressure, and the residue was purified by silica gel column chromatography to obtain the compound of interest as a pale yellow oil substance (1.59 g, 80%, E/Z mixture).
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