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A solution of 30 g <strong>[959236-59-0]7-fluoro-1H-indazole-3-carboxylic acid</strong> in 1200 mL dry methanol was added 8 mL concentrated sulfuric acid. The resulting mixture was heated to reflux and was continued over night. Reaction was allowed to cool to room temperature and was diluted with ethyl acetate (1000 mL). Organic solution was washed with saturated NaHCO3 (2×250 mL), brine (2×250 mL), dried (MgSO4), filtered and concentrated to a brown solid. Crude reaction was purified via MPLC (5%-30% ethyl ether/heptane) to afford 20.74 g (64%) of methyl 7-fluoro-1H-indazole-3-carboxylate as a bright yellow solid. 1H NMR (400 MHz, DMSO-d6) delta 14.49 (br s, 1H), 7.85-7.83 (m, 1H), 7.28-7.21 (m, 2H), 3.92 (s, 3H). MS (ESI) m/z 195 (M+H)+.
7-Fluoro-lH-indazole-3 -carboxylic acid (8.0 g) was dissolved in methanol (500 ml) . To the solution was added concentrated H2S04 (15 ml) at ice temperature, and the mixed solution was stirred under reflux for 7 hours. The solvent was removed under reduced pressure, chloroform was added to the residue, and the resultant was neutralized with saturated sodium bicarbonate aqueous solution. The organic layer was further washed with water, dried, and concentrated under reduced pressure. The residue was purified by silica-gel chromatography (column; Hi-Flash, developing solvent: hexane / ethyl acetate) and then purified again by silica-gel chromatography (column; Hi- Flash, developing solvent: chloroform / methanol) to give methyl 7-fluoro-lH-indazole-3-carboxylate (4.15 g) as a white crystal.
This compound was prepared following the procedure of Johnson, B. L.; Rodgers, J. D. Syn. Comm. 2005, 35, 2681-2684. A suspension of 5.28 g 7-fluoroisatin in 30 mL of water was added 1.30 g NaOH, in 10 mL water with stirring. The resulting dark red solution was stirred until all of the solids dissolved and was then cooled in an ice water bath. The solution was then slowly added a cooled (ice bath) solution of 2.21 g NaNO2 in 10 mL water. These combined solutions were then added slowly to cooled (ice bath) to solution of aqueous sulfuric acid (3.4 mL H2SO4 in 60 mL water). Ice was added to maintain a temperature of approximately 0 C. After stirring for approximately 10 minutes, this dark red diazonium solution was added slowly to a chilled (0 C., ice bath) solution of 18 g SnCl22H2O in 30 mL concentrated HCl. Ice was again added to maintain a temperature of approximately 0 C. After stirring for approximately 1 hour, the reaction was filtered and the resulting residue was dissolved in 1 N NaOH (60 mL), washed with ether (2×50 mL). The resulting yellow-brown solution was cooled in an ice bath and acidified to a pH3 (litmus paper) with concentrated HCl, which resulted in the formation of a dark yellow precipitate. The precipitate was collected by filtration, washed with water, and dried over night in an oven to give 3.69 g (47%) of 7-fluoro-1H-indazole-3-carboxylic acid as an orange solid. 1H NMR (400 MHz, DMSO-d6) delta 14.35 (br s, 1H), 13.22 (br s, 1H), 7.89-7.87 (m, 1H), 7.26-7.21 (m, 2H). MS (ESI) m/z 181 (M+H)+.
To a mixed solution of 7-fluoro-lH-indazole-3- carboxylic acid (15.0 g) and tetrahydrofuran (600 ml) were added pyridine (14.8 ml) and N, O-dimethylhydroxylamine (8.94 g) at ice temperature. The mixture was stirred for 1 hour, warmed to room temperature, and further stirred for 1 hour. To the reaction solution were added pyridine (13.4 ml) and l-ethyl-3 - (3 -dimethylaminopropyl) carbodiimide hydrochloride (31.9 g) , and the mixture was stirred at room temperature overnight. After the reaction was completed, the solvent was evaporated under reduced pressure. To the residue was added water (1.0 1), and the resultant crystal was collected on a filter to give 7-fluoro-N-methoxy-N- methyl-lH-indazole-3-carboxamide (12.4 g) as a yellow crystal.
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