Benzyl 9-methoxy-1,3-dioxo-1,2,3,6-tetrahydropyrrolo[3,4-c]carbazole-4-carboxylate → 9-Methoxy-1,3-dioxo-1,2,3,6-tetrahydropyrrolo[3,4-c]carbazole-4-carboxylic acid

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A solution of benzyl 9-methoxy-1,3-dioxo-1,2,3,6-tetrahydropyrrolo[3,4-c]carbazole-4-carboxylate (2.00 g), prepared as in example 3, in DMF/MeOH (4:1) (50 mL) containing 5% Pd-C (0.50 g) was hydrogenated at 60 psi for 2 h (Parr apparatus). The solution was filtered through a plug of Celite, which was washed 6 times with neat DMF followed by MeOH (several cycles). The combined filtrate and washings were concentrated to dryness in vacuo and the residue was slurried with diethyl ether to give the 9-methoxy-1,3-dioxo-1,2,3,6-tetrahydropyrrolo[3,4-c]carbazole-4-carboxylic acid (5) as a greenish solid. The reaction was repeated 5 times on this scale to and the products were combined to give 9-methoxy-1,3-dioxo-1,2,3,6-tetrahydropyrrolo[3,4-c]carbazole-4-carboxylic acid, (8.1 g, 84%). A portion of the product was purified by adsorption onto silica, followed by chromatography on silica, eluting with EtOAc. The product was triturated with diethyl ether to give 9-methoxy-1,3-dioxo-1,2,3,6-tetrahydropyrrolo[3,4-c]carbazole-4-carboxylic acid as an orange solid; mp>300° C. 1H NMR δ [(CD3)2SO] 12.15 (s, 1H), 8.42 (d, J=2.5 Hz, 1H), 7.97 (s, 1H), 7.57 (d, J=8.8 Hz, 1H0, 7.25 (dd, J=8.8, 2.5 Hz, 1H), 3.82 (s, 3H), 3.40 (br, 2H). Found: C, 58.69; H, 3.55; N, 8.40. C16H10N2O5,H2O requires C, 58.54; H, 3.68; N, 8.53.

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