Diethyl Oxalate → 4-(2-Methoxyphenyl)-2,4-dioxobutanoic acid

To a stirred solution of diethyl oxalate (16 g, 110 mmol) and sodium ethoxide (100 mL, 21% by wt. in ethanol, 300 mmol) was added dropwise a solution of 2-methoxy acetophenone (15 g, 100 mmol) in ethanol (100 mL). The reaction mixture was allowed to stir at ambient temperature overnight. The resulting solution was concentrated to approximately 50 mL on a rotary evaporator, followed by partitioning between diethyl ether (100 mL) and water (250 mL). The aqueous layer was adjusted to pH=3 with conc. HCl to give a suspension with a fine white precipitate, which was heated at 100° C. for 5-10 minutes followed by cooling in an ice bath for 1 h. The precipitate was filtered, washed with water (20 mL), and dried overnight under high vacuum to give 4-(2-methoxyphenyl)-2,4-dioxobutanoic acid. 1H NMR (300 MHz, CDCl3) δ 7.96 (q, J=9.0, 3.0 Hz, 1H), 7.53 (t, J=6.0 Hz, 1H), 7.47 (s, 0.9H keto form), 7.24 (s, 1.1H enol form), 7.06 (t, J=6.0 Hz, 1H), 7.00 (d, J=9.0 Hz, 1H), 3.97 (s, 3H). ESI-MS m/z 220.9 (M−H)−.