Synthesis of 2,3-Dioxo-2,3-dihydrobenzofurans – DMAP as Catalyst

D.J. Zwanenburg, W.A.P. Reynen, Synthesis, 624 (1976)

1. A solution of 2,5-dimethylphenol (12.2 g, 0.1 mol), oxalyl chloride (27. 94 g, 0.22 mol), DMAP (0.5 g, 4.1 mmol) in chloroform (300 mL) are heated under reflux for 10 h (no 2,5-dimethylphenol detected by glc). 

2. The reaction mixture is concentrated, the oily residue dissolved in 1,2-dichloroethane (100 mL) and dropped into a stirred suspension of aluminum chloride (40 g, 0.3 mol) in 1,2-dichloroethane (300 mL) at room temperature.

3. After 10 h the reaction mixture is hydrolyzed with water (100 mL), extracted with 1,2-dichloroethane, dried (molecular sieves, 4 A) and concentrated.  The yellow-red residue is purified by column chromatography (silica 0.05 - 0.2 mm, eluent: chloroform).  Appropriate fractions are combined, evaporated and the residue crystallized from petroleum ether to give 4,7-dimethyl-2,3-dioxo-2.3-dihydrobenzofuran (b.p. 40-60°C).  Yield 80%.