[NH2:1][C:2]1[CH:3]=[CH:4][C:5]2[N:9]=[C:8]3[CH2:10][CH2:11][CH2:12][N:7]3[C:6]=2[CH:13]=1.[C:14](OC(=O)C)(=[O:16])[CH3:15]>C1C=CC=CC=1>[C:14]([NH:1][C:2]1[CH:3]=[CH:4][C:5]2[N:9]=[C:8]3[CH2:10][CH2:11][CH2:12][N:7]3[C:6]=2[CH:13]=1)(=[O:16])[CH3:15]8.65 g of 7-amino-2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole (2A00) prepared according to W. Reppe Ann. 596 (1955) p. 209 are suspended in 50 cm3 of benzene. To this suspension is added dropwise 6.2 g of acetic anhydride. The mixture is boiled for 15 min and after cooling the precipitated acetyl compound is sucked off. Recrystallization from ethanol yields 7.3 g of 7-acetylamino-2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole. Melting point: 250°-255°C. Two further recrystallizations from ethanol raise the melting point to 260°-262°C.
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