[C:1](=O)([O-])[O-].[K+].[K+].C=O.[C:9]([O:13][C:14](=[O:36])[CH:15](P(OCC)(OCC)=O)[CH:16]([C:18]1[CH:27]=[CH:26][C:21]([C:22]([O:24][CH3:25])=[O:23])=[CH:20][CH:19]=1)[CH3:17])([CH3:12])([CH3:11])[CH3:10]>C1COCC1>[C:9]([O:13][C:14]([C:15](=[CH2:1])[CH:16]([C:18]1[CH:19]=[CH:20][C:21]([C:22]([O:24][CH3:25])=[O:23])=[CH:26][CH:27]=1)[CH3:17])=[O:36])([CH3:10])([CH3:11])[CH3:12]Potassium carbonate (9.16 g, 66.2 mmol) and paraformaldehyde (2.48 g, 82.7 mmol) were added to a solution of methyl 4-(4-(tert-butoxy)-3-(diethoxyphosphoryl)-4-oxobutan-2-yl)benzoate (13.7 g, 33.1 mmol) in anhydrous THF (250 mL), respectively. The reaction mixture was heated at reflux for 20 h, then cooled, and concentrated. The residue was purified by flash chromatography on silica gel eluting with 5% ethyl acetate in petroleum ether to give the title compound. MS: m/z=235.0 (M−tBu); 1H NMR (400 MHz, CDCl3): δ 7.97 (d, 2H, J=8.5 Hz), 7.28 (d, 2H, J=8.5 Hz), 6.26-6.32 (m, 1H), 5.56-5.61 (m, 1H), 4.01 (q, 1H, J=7.1 Hz), 3.92 (s, 3H), 1.42 (d, 3H, J=7.0 Hz), 1.33 (s, 9H).
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