Potassium Carbonate → 12-(2,2-dimethyl-1,3-dioxolan-4-ylmethyl)-6,7,12,13-tetrahydro-6-methyl-5,7-dioxo-5H-indolo[2,3-a]pyrrolo-[3,4-c]carbazole

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12-(2,2-Dimethyl-1,3-dioxolan-4-ylmethyl)-6,7,12,13-tetrahydro-6-methyl-5,7-dioxo-5H-indolo-[2,3-a]pyrrolo[3,4-c]carbazole is prepared in the following manner: 3g (8.84 mmol) 6,7,12,13-Tetrahydro-6-methyl-5,1-dioxo-5H-indolo[2,3-a]pyrrolo[3,4-c]carbazole (precursor for Example 5) are stirred for 2 hours at 20° C. with 595 mg (9 mmol) powdered potassium hydroxide, 620 mg (4.5 mmol) potassium carbonate and 300 mg (1.1 mmol) 18-crown-6 in 200 ml toluene under an atmosphere of nitrogen. Subsequently, 2.6 g (9 mmol) 2,2-dimethyl-4-(4-methylphenylsulphonyloxymethyl)-1,3-dioxolan (see Biochemistry, 1971, 10, 3204) are added thereto and the reaction mixture is heated under reflux for 16 hours. After cooling, the reaction mixture is evaporated in a vacuum and the residue is taken up in ethyl acetate and water. The ethyl acetate solution is separated off, washed with water, dried over anhydrous sodium sulphate, filtered and evaporated. The residue is chromatographed on silica gel with toluene/acetone (9:1 v/v), the fraction with the Rf 0.65 in toluene/acetone (3:1 v/v) is isolated, stirred with 20 ml diisopropyl ether/acetone (4:1 v/v) and the yellow crystals formed of 12-(2,2-dimethyl-1,3-dioxolan-4-ylmethyl)-6,7,12,13-tetrahydro-6-methyl-5,7-dioxo-5H-indolo[2,3-a]pyrrolo-[3,4-c]carbazole filtered off.

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