Diethyl Oxalate → Ethyl 8-isopropyl-4-oxo-4h-chromene-2-carboxylate

Participants

Reaction Steps

To a solution of Example 13A (2.048 g, 11.5 mmol) in ethanol (60 mL)was added diethyl oxalate (3.43 mL, 25.3 mmol) and sodium ethoxide (21% in EtOH, 12.9 mL, 34.5 mmol) and the mixture was refluxed for 30 minutes. The mixture was cooled to ambient temperature, partitioned between diethyl ether (150 mL) and water (150 mL). Hydrochloric acid (12N, 3 mL) was added and the separated organic layer was washed with brine, dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure to afford ethyl 8-isopropyl-4-oxo-4H-chromene-2-carboxylate. After dissolving the intermediate in acetic acid (45 mL) and 12N hydrochloric acid (7.5 mL), the mixture was heated to reflux for 5.5 hours then cooled to ambient temperature. Water (400 mL) was added and the mixture was extracted with ethyl acetate (400 mL). The combined organic layers were washed with water (400 mL) and brine, dried over anhydrous sodium sulfate and filtered. The solution was concentrated under reduced pressure and vacuum dried overnight to afford the title compound. 1H NMR (300 MHz, DMSO-d6) δ ppm 1.32 (d, 6H), 3.56 (m, 1H), 6.91 (s, 1H), 7.48 (t, 1H), 7.78 (dd, 1H), 7.89 (dd, 1H). MS (ESI) m/z 232.94 (M+H)+.

Provenance & Evidence