Triethylamine → 4-Amino-9-methoxypyrrolo[3,4-c]carbazole-1,3(2H,6H)-dione

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Diphenylphosphoryl azide (1.81 mL, 8.38 mmol) was added to a mixture of the 9-methoxy-1,3-dioxo-1,2,3,6-tetrahydropyrrolo[3,4-c]carbazole-4-carboxylic acid (2.55 g, 8.22 mmol), prepared as in example 4, and Et3N (1.17 mL, 8.38 mmol) in anhydrous t-butanol (300 mL) and the mixture was refluxed under an atmosphere of nitrogen for 16 h. The solution was concentrated in vacuo and the residue partitioned between EtOAc and saturated aqueous NaHCO3. Insoluble material was removed by filtration of the two layers through Celite, washing through with more EtOAc. The organic phase was dried, the drying agent was removed and the solution was concentrated to dryness and gave a yellow solid. This material was dissolved in CH2Cl2/trifluoroacetic acid (1:1) (200 mL) and the solution was held at room temperature for 1 h. After concentration in vacuo the residue was partitioned between EtOAc and saturated aqueous NaHCO3 solution. The EtOAc solution was dried, the drying agent was removed and the solution was concentrated to dryness to give an orange solid which was adsorbed onto silica and chromatographed. Elution with ethyl acetate/petroleum ether (1:1) followed by ethyl acetate and then methanol/ethyl acetate (1:9) gave 4-amino-9-methoxypyrrolo[3,4-c]carbazole-1,3(2H,6H)-dione (6) as an orange powder (2.16 g, 93%), mp 342–345° C. 1H NMR δ [(CD3)2SO] 11.18 (s, 1H), 10.78 (br s, 1H), 8.18 (d, J=2.5 Hz, 1H), 7.29 (d, J=8.7 Hz, 1H), 7.01 (dd, J=8.7, 2.5 Hz, 1H), 6.83 (s, 1H), 6.28 (br s, 2H), 3.82 (s, 3H). Found: C, 63.05; H, 3.99; N, 14.05. C15H11N3O3, 1/2H2O requires C, 63.04; H, 4.06; N, 14.7.

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