[H-].[Na+].[CH2:3]1[O:13][C:12]2[C:5](=[C:6]([CH:9]=[CH:10][CH:11]=2)[CH:7]=O)[O:4]1.[OH2:14].[O:15]1[CH2:19][CH2:18][CH2:17][CH2:16]1>>[CH2:3]1[O:13][C:12]2[C:5](=[C:6]([CH:9]=[CH:10][CH:11]=2)[CH:7]=[CH:17][C:16]([O:15][CH2:19][CH3:18])=[O:14])[O:4]1Triethyl phosphonoacetate (4.05 mL, 20.2 mmol) was added dropwise to a stirred suspension of sodium hydride (0.80 g, 20 mmol) in anhydrous tetrahydrofuran (20 mL) at 0° C. under nitrogen. The mixture was stirred at 0° C. for 20 minutes. A solution of 2,3-methylenedioxybenzaldehyde (2.50 g, 16 mmol) in tetrahydrofuran (10 mL) was added dropwise at 0° C. The mixture was stirred for 2 hours during which time it was allowed to warm to room temperature. The mixture was poured into water (250 mL), and extracted with ethyl acetate (3×250 mL). The combined organic extracts were then washed with brine, dried (MgSO4) and concentrated in vacuo. The crude product was chromatographed over silica gel. Elution with ethyl acetate/hexanes (1:10) gave ethyl 2,3-methylenedioxycinnamate as a colourless solid (3.50 g, 92%).
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