In a 500 ml round-bottom flask, 8 grams (33.3 mmoles) of 2-acetyl-naphtho[2,3-b]furan-4,9-dione (prepared in example 2 or 3) was dissolved in 150 ml of DMF with heating. To the solution, added 14 ml of TEA, 8 grams of zinc powder, 1 gram of tetrabutylammonium bromide and 29 grams (166.7 mmoles) of sodium hydrosulfite. The mixture was sealed or isolated from air. Then 17 grams (166.7 mmoles) of acetic anhydride was added with syringe, and the resulting mixture had been stirred vigorously at room temperature for 3 hours. After addition of 300 ml of ethyl acetate, the reaction mixture was filtered, and the solid was washed with 200 ml of ethyl acetate. The filtrates were combined, extracted with 300 ml of ice-cooled aqueous 3% citric acid solution twice, and dried with anhydrous sodium sulfate. The organic phase was evaporated to dryness. The residue was washed with 60 ml of ice-cooled ethanol, and then filtered solid was crystallized in 250 ml of ethanol. 5.5 grams (16.9 mmoles, yield 50.7%) of product was obtained and characterized by 1H NMR and mass spectrum. 1H NMR (in CDCl3) δ 2.59 (s, 3H), 2.62 (s, 3H), 2.66 (s, 3H), 7.50 (s, 1H), 7.53-7.62 (m, 2H), 8.00-8.03 (m, 2H). Mass (M+H) is 327, Mass (M+Na) is 349.
