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To a solution of 2-amino-3-nitro-4-(2-thienyl)pyridine (2.06 g, 9.3 mmol) and 10% palladium-carbon (466 mg) in ethanol (130 ml)-ethyl acetate (65 ml), a 1 M aqueous sodium borohydride solution was added at 0° C. The mixture was stirred at 0° C. for 1 hour and then poured into a 5% aqueous ammonium chloride solution (43 ml). The mixture was filtered through celite, and the filtrate was diluted with water (500 ml) and extracted three times with ethyl acetate (250 ml). The solution was dried over sodium sulfate and then evaporated under reduced pressure to remove the solvent. The residue was purified by column chromatography (methylene chloride:ethanol=19:1 to 93:7) to give 2,3-diamino-4-(2-thienyl)pyridine (Rf 0.24/methylene chloride:ethanol=9:1) (1.46 g, yield 82%).

1. filtrationThe mixture was filtered through celite
2. additionthe filtrate was diluted with water (500 ml)
3. extractionextracted three times with ethyl acetate (250 ml)
4. dry with materialThe solution was dried over sodium sulfate
5. customevaporated under reduced pressure
6. customto remove the solvent
7. customThe residue was purified by column chromatography (methylene chloride:ethanol=19:1 to 93:7)