[H-].[Na+].[CH3:3][O:4][C:5]([CH2:7]P(OC)(OC)=O)=[O:6].[OH:14][C:15]1[CH:20]=[C:19]([CH2:21][CH2:22][CH2:23][CH:24]=O)[O:18][C:17](=[O:26])[C:16]=1[C:27](=[O:30])[CH2:28][CH3:29]>C1COCC1>[OH:14][C:15]1[CH:20]=[C:19]([CH2:21][CH2:22][CH2:23]/[CH:24]=[CH:7]/[C:5]([O:4][CH3:3])=[O:6])[O:18][C:17](=[O:26])[C:16]=1[C:27](=[O:30])[CH2:28][CH3:29]NaH (0.4 g; 10 mmol; 60% dispersion in mineral oil; Aldrich) was added to trimethyl phosphonoacetate (1.90 g; 10 mmol; Aldrich) in 25 ml THF. The reaction was stirred at 25° C. for 15 min, after which 4-(4-hydroxy-2-oxo-3-propionyl-2H-pyran-6-yl)butanal (XVI; 1.01 g; 4.3 mmol) in 40 ml THF was added. The reaction mixture was stirred at 25° C. for 2 h, quenched with saturated NH4Cl, extracted with 3×30 ml EtOAc, dried with anhydrous Na2SO4, and evaporated. The product was purified via silica flash chromatography (EtOAc gradient in hexanes).
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