To a pre-dried two-necked round-bottomed flask were added 1,2-methylenedioxybenzene (piperylene ring, 2.0 g, 16.37 mmol), 1,2-dichloroethane (7 mL) and n-butyric anhydride (3.2 mL, 19.6 mmol). The reaction mixture was cooled to -10 °C and boron trifluoride ethyl ether complex (BF3-Et2O, 6.78 g, 47.7 mmol) was slowly added dropwise over 15 min while keeping the reaction temperature between -5 °C and 0 °C. After the dropwise addition, the reaction mixture was continued to be stirred at -5 °C for 3 hours. Upon completion of the reaction, the reaction was quenched with saturated aqueous sodium acetate solution, and the organic layer was separated and washed sequentially with 5% aqueous sodium hydroxide solution (7 mL) and deionized water. The organic layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure to obtain the crude product. The crude product was purified by silica gel column chromatography with hexane/ethyl acetate (10:1, v/v) as eluent to afford the target compound 3,4-(methylenedioxy)phenylbutanone (1.34 g, 85% yield).
1H NMR (400 MHz, CDCl3) δ: 7.52 (dd, J = 8.1, 1.6 Hz, 1H), 7.40 (d, J = 8.1 Hz, 1H), 6.80 (d, J = 8.1 Hz, 1H), 5.99 (s, 1H), 2.82 (t, J = 7.3 Hz, 2H), 1.70 (h, J = 7.4 Hz, 2H ), 0.95 (t, J = 7.4 Hz, 3H).
13C NMR (100 MHz, CDCl3) δ: 198.4, 151.5, 148.1, 132.0, 124.1, 107.8, 107.7, 101.7, 40.2, 18.0, 13.8.
HRMS-ESI-MS (m/z) [M + H]+: calculated value C11H13O3: 193.0865; measured value: 193.0867.
