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Stage #1: With mercury(II) oxide In tetrachloromethane at 20℃; Heating / reflux; Irradiation Stage #2: With bromine In tetrachloromethane for 0.166667 h; Heating / reflux
To a solution of the mixture of 2, 5-difluoro-3-nitro-benzoic acid and 3,6- difluoro-2-nitro-benzoic acid (2.48 g, 12.2 mmol, ratio 2: 1) in carbon tetrachloride (60 ML) was added mercury (II) oxide (red) (5.2 g, 24 mmol) at room temperature. The mixture was heated to reflux and irradiated with light. Bromine (3.8 g, 24 mmol) was added dropwise to the mixture in 10 minutes. The reaction mixture was heated at reflux for 6 hours. After cooling, the solid was removed by filtration and the filtrate was washed with saturated sodium bicarbonate and water. After removal of the solvent, the residue was purified by chromatography using hexane/ethyl acetate (8: 1) to give the title compound. Yield 1.07 g (38percent). LH NMR (400 MHZ, CDCl3) : 8 7.76 (ddd, 1H), 7.64 (ddd, 1H).
To a mixture of 1-BROM-2, 5-difluoro-3-nitro-benzene (1.0 g, 4.2 mmol) and pent-4-ynoic acid methyl ester (0.94 g, 8.4 mmol) were added palladium (II) acetate (0.094 g, 0.42 mmol), triphenylphosphine (0.22 g, 0.84 mmol) and copper (I) iodide (0.08 g, 0.42 mmol). The mixture was stirred at room temperature under nitrogen atmosphere for 20 minutes and then treated with triethylamine (8 mL). The mixture was heated to reflux for 4 hours. After removal of the triethylamine, the residue was diluted with ethyl acetate (50 mL). The solid was removed by filtration. The filtrate was concentrated and purified by chromatography using hexane/ethyl acetate (8: 1 to 4: 1) as eluent to give the title compound in 72 % yield (0.81 G). LH NMR (400 MHZ, CDC13) : 8 7.68 (ddd, 1H), 7.38 (ddd, 1H), 3.74 (s, 3H), 2.81 (t, 2H), 2.67 (t, 2H).
To a solution of the mixture of 2, 5-difluoro-3-nitro-benzoic acid and 3,6- difluoro-2-nitro-benzoic acid (2.48 g, 12.2 mmol, ratio 2: 1) in carbon tetrachloride (60 ML) was added mercury (II) oxide (red) (5.2 g, 24 mmol) at room temperature. The mixture was heated to reflux and irradiated with light. Bromine (3.8 g, 24 mmol) was added dropwise to the mixture in 10 minutes. The reaction mixture was heated at reflux for 6 hours. After cooling, the solid was removed by filtration and the filtrate was washed with saturated sodium bicarbonate and water. After removal of the solvent, the residue was purified by chromatography using hexane/ethyl acetate (8: 1) to give the title compound. Yield 1.07 g (38%). LH NMR (400 MHZ, CDCl3) : 8 7.76 (ddd, 1H), 7.64 (ddd, 1H).
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