Dimethylformamide → 3-Methoxyfuran-2-carbaldehyde

A 3-L, one-necked, round-bottomed flask was equipped with a Teflon-coated magnetic stirbar. The system was flame-dried and flushed with argon. The flask was charged with a solution of N,N-dimethylformamide (31.9 mL, 413 mmol, 1.35 equiv) in dichloromethane (1.2 L). The solution was cooled to 0° C. in a dry ice-acetone bath, and then oxalyl chloride (32.5 mL, 367 mmol, 1.2 equiv) was added over 16 min. Vigorous bubbling occurred and a white solid precipitated. After stirring for 20 min, the reaction mixture was cooled to −40° C. by addition of dry ice to the cooling bath and a solution of 3-methoxyfuran (Meister, C.; Scharf, H.-D. Synthesis 1981, 737-739) (30 g, 306 mmol, 1 equiv) in dichloromethane (100 mL) was added via cannula. A dark-brown color formed during the addition. After stirring for 20 min, the cooling bath was removed and saturated aqueous sodium bicarbonate solution (1.5 L) was added. The biphasic mixture was stirred vigorously for 6 hours, and then was partitioned. The aqueous layer was further extracted with dichloromethane (2×800 mL). The organic layers were combined and the combined layers were dried over sodium sulfate. The solids were filtered and the filtrate was concentrated. The residue obtained was purified by flash-column chromatography on silica gel (100% diethyl ether) to furnish 3-methoxyfurfural 6 (21.2 g, 55%) as a light-yellow solid.