Hydrochloric Acid → 7-fluoro-3,4-dihydro-2H-1-benzopyran-4-one

Participants

Reaction Steps

To a solution of 3-(3-fluorophenoxy)-propionic acid (4.94 g, 26.8 mmol) in dichloromethane (135 mL) is added several drops of anhydrous dimethylformamide, followed by oxalyl chloride (4.68 mL, 53.6 mmol). The reaction is stirred at room temperature until gas evolution ceases (˜30 min), then evaporated under reduced pressure and reconstituted in dichloromethane (135 mL). Following the addition of aluminum trichloride (4.28 g, 32.1 mmol), the reaction is stirred for 1 h, then 2 M aqueous hydrochloric acid (100 mL) and dichloromethane (100 mL) are added. The layers are separated, and the aqueous layer extracted with dichloromethane (2×100 mL). The combined organic-layers are washed with brine (2×100 mL), dried over magnesium sulfate, filtered and evaporated under reduced pressure. The crude residue is recrystallized twice from 2-propanol to afford slightly impure title compound (1.79 g, 40%), and the mother liquor subjected to flash chromatography (silica gel, 3:1 pentane/Et2O) to afford pure title compound (1.15 g, 26%): Rf 0.45 (1:1 ethyl acetate/hexanes); mp 53-56 ° C.; 1 H NMR (300 MHz, CDCl3), δ2.75 (t, J=6.4 Hz, 2H), 4.51 (t, J=6.4 Hz, 2H), 6.61 (dd, J=2.3, 9.9 Hz, 1H), 6.65-6.72 (m, 1H), 7.87 (dd, J=6.7, 8.8 Hz, 1H); 19F NMR (282 MHz, CDCl3), δ-101.06; APCI MS m/z 167 [C9H7FO2+H]+.

Provenance & Evidence