[N+:1]([C:4]1[CH:5]=[CH:6][C:7]2[O:11][C:10]([C:12]([OH:14])=[O:13])=[CH:9][C:8]=2[CH:15]=1)([O-:3])=[O:2].[CH3:16]N(C=O)C.C(Cl)(C(Cl)=O)=O.N1C=CC=CC=1>C(Cl)Cl.CO>[CH3:16][O:13][C:12]([C:10]1[O:11][C:7]2[CH:6]=[CH:5][C:4]([N+:1]([O-:3])=[O:2])=[CH:15][C:8]=2[CH:9]=1)=[O:14]To a suspension of 5-nitro-2-benzofurancarboxylic acid (5 g, 24.15 mmol) in CH2Cl2 (250 mL) at 0° C. was added DMF (0.100 mL) followed by (COCl)2 (2M in CH2Cl2, 36.23 mL, 72.46 mL) over a period of 10 min. The reaction was stirred at 0° C. for 1 h and then at room temperature for 30 min. The reaction solvent was removed under a reduced pressure, dried under high vacuum and again suspended in CH2Cl2 (250 mL). The solution was cooled to 0° C., were added pyridine (4.8 mL, 48.03 mmol) followed by MeOH (10 mL, excess) and stirred overnight. The extractive work-up with CH2Cl2 gave the expected 2-methoxycarbonyl-5-nitrobenzofuran (R926609). 1H NMR (CDCl3): δ 8.66 (d, 1H, J=2.4 Hz), 8.36 (dd, 1H, J=2.4 and 9.6 Hz), 7.71 (d, 1H, J=9.3 Hz), 7.65 (s, 1H), 4.01 (s, 3H); LCMS: ret. time: 26.94 min.
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