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0 °C

To a solution of 4-bromo-1H-pyrrole-2-carboxylic acid methyl ester (3.5 g, 17.2 mmol, 1 eq) in DMF (120 mL) was added NaH (0.82 g, 20.6 mmol, 1.2 eq) at 0° C., and the mixture was stirred at 0° C. for 1 h, followed by the addition of o-(diphenylphosphinyl)-hydroxylamine (6 g, 25.8 mmol). The reaction mixture was stirred for another 1 h, then neutralized with 20% NH4Cl solution, and extracted with EA. The combined organic layers were washed with water and brine, dried over sodium sulfate, filtered, and concentrated by evaporation. The residue was purified by column chromatography on silica gel (PE/EA=4:1) to give 1-amino-4-bromo-1H-pyrrole-2-carboxylic acid methyl ester (2.9 g, yield 77%) as a light yellow solid. MS (ES+) requires: 218, 220. found 219, 221 [M+H]+; purity: 97%.

1. stirringThe reaction mixture was stirred for another 1 h
2. extractionextracted with EA
3. washThe combined organic layers were washed with water and brine
4. dry with materialdried over sodium sulfate
5. filtrationfiltered
6. concentrationconcentrated by evaporation
7. customThe residue was purified by column chromatography on silica gel (PE/EA=4:1)