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0 °C

To a solution of 1-(3-methyl-butylamino)-1H-pyrrole-2-carboxylic acid (Example 1d, 0.25 g, 1.27 mmol) in water (2 mL) was added potassium carbonate (0.175 g, 1.27 mmol). The reaction mixture was cooled to 0° C. and phosgene (20% solution in toluene) (0.95 mL, 1.91 mmol) was slowly added dropwise. The resulting yellow solution was stirred for 16 h. Ethyl acetate (4 mL) was added and the layers were separated. The aqueous layer was extracted with ethyl acetate (3×5 mL). The combined organic layers were dried over magnesium sulfate, filtered and concentrated in vacuo. The crude product was purified by column chromatography (Merck silica gel 60, 40-63 μm, ethyl acetate/hexane, 20-50%) to afford the desired product, 4-(3-methyl-butyl)-6-oxa-3a,4-diaza-indene-5,7-dione (0.16 g, 0.72 mmol, 57% yield) as a tan solid. 1H NMR (400 MHz, DMSO-d6) δ 0.93 (6H, d, J=6.8 Hz), 1.56 (2H, m), 1.65 (1H, m), 4.16 (2H, t, J=7.2 Hz), 6.50 (1H, m), 7.08 (1H, m), 7.70 (1H, m).

1. customthe layers were separated
2. extractionThe aqueous layer was extracted with ethyl acetate (3×5 mL)
3. dry with materialThe combined organic layers were dried over magnesium sulfate
4. filtrationfiltered
5. concentrationconcentrated in vacuo
6. customThe crude product was purified by column chromatography (Merck silica gel 60, 40-63 μm, ethyl acetate/hexane, 20-50%)