To a mixture of methyl 2-(3,4-methylenedioxyphenyl)propionate (1 g, 4.8 mmol) in 1,2-dichloroethane (50 mL) was added piperonylic acid (1.6 g, 9.6 mmol) and P2O5 (4 g). The reaction mixture was stirred for 15 h and then poured to ice water (200 mL) and the product was extracted with EtOAc (2×100 mL). The pure product was obtained by flash chromatography (453 mg, 27%). 1H NMR (CDCl3) 7.37 (s, 1H), 7.33 (d, J=8.0, 1H), 6.95 (s, 1H), 6.83 (d, J=8.0, 1H), 6.76 (s, 1H), 6.07 (s, 2H), 6.02 (s, 2H), 3.95 (q, J=7.1, 1H), 3.58 (s, 3H), 1.45 (d, J=7.1, 3H).
