The general procedure for the synthesis of ethyl 7-hydroxy-2-oxo-2H-benzopyran-3-carboxylate from 2,4-dihydroxybenzaldehyde (3.70 mmol) and diethyl malonate (7.90 mmol) was as follows: piperidine (10 drops) was added to a solution of diethyl malonate of 2,4-dihydroxybenzaldehyde and the resulting mixture was stirred and reacted for 2 hours at room temperature. Upon completion of the reaction, the reaction mixture was acidified with 10% aqueous hydrochloric acid solution (5 mL). The precipitated solid was collected by filtration and washed with cold water (10 mL). The crude product was purified by fast column chromatography using dichloromethane:ethyl acetate (70:30, v/v) as eluent to afford the target compound ethyl 7-hydroxy-2-oxo-2H-chromene-3-carboxylate (0.735 g, 97% yield). The structure of the product was confirmed by 1H NMR (400 MHz, DMSO-d6) and 13C NMR (100 MHz, DMSO-d6): 1H NMR δ 1.28 (t, J = 7.1 Hz, 3H), 4.24 (q, J = 7.1 Hz, 2H), 6.71 (d, J = 1.8 Hz, 1H), 6.83 (dd, J = 1.8, 8.3 Hz, 1H), 7.74 (d, J = 8.3 Hz, 1H), 8.66 (s, 1H), 11.07 (s, 1H); 13C NMR δ 14.1, 60.8, 101.7, 110.4, 113.9, 120.0, 132.1, 149.4, 156.3, 157.0, 162.9, 164.0.
