In a 250 ml round-bottom flask, 2 grams (8.3 mmoles) of 2-acetyl-naphtho[2,3-b]furan-4,9-dione (prepared in example 2 or 3) was dissolved in 50 ml of DMF with heating. To the solution, added 3.5 ml of TEA, 2 grams of zinc powder, 0.3 gram of tetrabutylammonium bromide, 2.33 grams (13.3 mmoles) of [(tert-butoxycarbonyl)amino]acetic acid, 5.04 grams (13.3 mmoles) of N,N,N′,N′-Tetramethyl-O-(1H-benzotriazol-1-yl)uronium hexafluorophosphate (HBTU) and 7.25 grams (41.7 mmoles) of sodium hydrosulfite. The mixture was sealed or isolated from air, and then had been stirred vigorously at room temperature overnight. After addition of 100 ml of ethyl acetate, the reaction mixture was filtered, and the solid was washed with 50 ml of ethyl acetate. The filtrates were combined, extracted with 100 ml of ice-cooled aqueous 3% citric acid solution twice, and dried with anhydrous sodium sulfate. The organic phase was evaporated to dryness. Product was purified by silica gel chromatograph using dichloromethane/ethyl acetate (4:1) as elution solvent. 1.64 gram (4.1 mmoles) of product was obtained with yield of 49.4% and characterized by 1H NMR and mass spectrum. 1H NMR (in DMSO) δ 1.44 (s, 9H), 2.59 (s, 3H), 4.28 (d, J=6, 2H), 7.49-7.65 (m, 3H), 7.97 (m, 1H), 8.20-8.35 (m, 2H), 11.4 (s, 1H). Mass (M+H) is 400, Mass [M-(tert-butyl)+2H] is 344.
