The general procedure for the synthesis of 7-chloro-4-oxo-4H-chromene-2-carboxylic acid from ethyl 7-chloro-4-oxo-4H-chromene-2-carboxylate was as follows: an aqueous 6M HCl solution (2 mL) was added to a solution of ethyl 7-chloro-4-oxo-4H-chromene-2-carboxylate in acetic acid (4 mL) and the mixture was heated to 80 °C and kept for 4.5 hours. After completion of the reaction, the mixture was cooled to room temperature, diluted with distilled water (6 mL), the resulting beige precipitate (204 mg, 89% yield) was collected by filtration and dried under reduced pressure at 50 °C. The product was characterized by 1H NMR (300 MHz, DMSO-d6): δ 6.92 (s, 1H), 7.58 (dd, J = 8.65,1.86 Hz, 1H), 7.95 (d, J = 1.70 Hz, 1H), 8.04 (d, J = 8.48 Hz, 1H); mass spectrum (APCI) m/z 225 [M + H]+, 224 [ M-H]+, 178.9 [M-CO2H]+.
