Trifluoroacetic acid → 5-chloro-6-(2,3-dichlorophenyl)-2-(trifluoromethyl)-1H-imidazo[4,5-b]pyridine

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Reaction Steps

To a solution of 6-chloro-3-nitropyridin-2-amine (630 mg, 3.63 mmol) in ethanol (11 mL) was add I2 (920 mg, 3.62 mmol) and Ag2SO4 (1132 mg, 3.63 mmol).). The resulting solution was stirred overnight at room temperature and dissolved in water (100 mL), then extracted with ethyl acetate (3×80 ml). The combined organic layers were washed with brine (50 ml), dried over anhydrous sodium sulfate and concentrated under vacuum to produce 6-chloro-5-iodo-3-nitropyridin-2-amine as a yellow solid (640 mg, 59%). Next, to a solution of 6-chloro-5-iodo-3-nitropyridin-2-amine (640 mg, 2.14 mmol) in ethanol (40 ml) and water (10 ml) was added Fe powder (1.93 g, 34.46 mmol) and NH4Cl (887 mg, 16.58 mmol). The resulting solution was heated to reflux for 4 h and then concentrated. The residue was dissolved in water (100 mL) and extracted with ethyl acetate (3×80 ml). The combined organic layers was washed with brine (50 mL), dried over anhydrous sodium sulfate and concentrated under vacuum. The residue was purified by a silica gel column with 33% ethyl acetate in petroleum ether to produce 6-chloro-5-iodopyridine-2,3-diamine as a brown solid (560 mg, 97%). The mixture of 6-chloro-5-iodopyridine-2,3-diamine (100 mg, 0.37 mmol), (2,3-dichlorophenyl)boronic acid (147.3 mg, 0.77 mmol), Pd(Ph3P)4 (42.9 mg, 0.04 mmol) and sodium carbonate (118.2 mg, 1.12 mmol) in water (5 mL) and dioxane (15 mL) was heated to reflux overnight. Then the resulting solution was quenched with water (100 mL) and extracted with ethyl acetate (3×50 ml). The combined organic layers were washed with brine (50 mL), dried over anhydrous sodium sulfate and concentrated under vacuum. The residue was purified by a silica gel column with 50% ethyl acetate in petroleum ether to produce 6-chloro-5-(2,3-dichlorophenyl)pyridine-2,3-diamine as a brown solid (80 mg, 75%). Finally, the solution of 6-chloro-5-(2,3-dichlorophenyl)pyridine-2,3-diamine (80 mg, 0.28 mmol) in trifluoroacetic acid (10 mL) and hydrochloric acid (conc., 2 mL) was heated to reflux overnight. Then the resulting mixture was quenched with water (100 mL), adjusted pH to 8 with sodium carbonate and extracted with ethyl acetate (3×80 mL). The combined organic layers was dried over anhydrous magnesium sulfate and concentrated to give a residue, which was purified by a silica gel column with 50% ethyl acetate in petroleum ether to produce 5-chloro-6-(2,3-dichlorophenyl)-2-(trifluoromethyl)-1H-imidazo[4,5-b]pyridine. Trifluoroacetic acid as a off-white solid (2 mg, 2%).

Provenance & Evidence