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Stage #1: With water; potassium hydroxide In tetrahydrofuran; methanol at 20℃; for 16 h; Stage #2: With acetic acid In tetrahydrofuran; methanol
b: furo[2,3-clpyridine-2-carboxylic acid:To a solution of ethyl furo[2,3-c]pyridine-2-carboxylate (3.82 g, 19.98 mmol) in water:THF:MeOH (1 : 1 : 1 , 60 mL) was added potassium hydroxide (3.36 g, 59.9 mmol) and the resulting mixture was stirred at ambient temperature for 16 hours. The solvent volume was then reduced to ~20 mL and acetic acid was added until pH ~4. The solids were collected by vacuum filtration, washed twice with water, and dried in a vacuum oven overnight to afford the title compound (2.90 g, 89percent). 1H NMR (DMSO-de): δ 9.09 (s, 1H), 8.47 (d, 1H), 7.81 (dd, 1H), 7.71 (d, 1H), 3.36 (br s, 1H).
75%
With water; potassium hydroxide In tetrahydrofuran; methanol at 20℃; for 16 h;
Step 6. To a solution of ethyl furo[2,3-c]pyridine-2-carboxylate (158 g, 0.83 mol) in water:THF:MeOH (1:1:1, 2.4 L) was added KOH (139 g, 2.49 mol). Thereaction mixture was stirred at rt for 16 h and then concentrated to a volume of 750 mL. To this residue was added acetic acid until pH 4. The resulting solids were collected by filtration, washed with water (300 mLx2) and dried in a vacuum oven overnight to give the title compound (101 g, 75percent) as a pale yellow solid. 1H NMR (400 MHz, DMSO-d6) 6 9.07 (s, 1H), 8,47 (d, J 5.6 Hz, 1H), 7.80 (d, J = 5.2 Hz,1H), 7.61 (s, 1H). MS (ESI+) m/z: 164 [M+F]+
75%
With water; potassium hydroxide In tetrahydrofuran; methanol at 20℃; for 16 h;
Step 6. To a solution of ethyl furo[2,3-cjpyridine-2-carboxylate (158 g, 0.83 mol) in water:THF:MeOH (I: 1:1, 2.4 L) was added KOH (139 g, 2.49 mol). Thereaction mixture was stirred at ii for 1 6 h and then concentrated to a volume of 750 mL. To this residue was added acetic acid until pH 4. The resulting solids were collected by filtration, washed with water (300 mLx2) and dried in a vacuum oven overnight to give the title compound (101 g, 75percent) as a pale yellow solid. 1H NMR (400 Mi-Iz, DMSO-d6) 6 9.07 (s, In), 8,47 (d, J 5.6 Hz, I H), 7.80 (d, J = 5.2 Hz,1H), 7.61 (s, IH). MS (ES1-b) ni z: 164 [M+F]+
75%
With water; potassium hydroxide In tetrahydrofuran; methanol at 20℃; for 16 h;
Step 6. To a solution of ethyl furo[2,3-c]pyridine-2-carboxylate ( 158 g, 0,83 mol) in water:THF:MeOH (1 : 1 : 1 , 2 4 L) was added KOH ( 139 g, 2.49 mol). The reaction mixture was stirred at rt for 1 6 h and then concentrated to a volume of 750 mL. To this residue was added acetic acid until pH ~ 4. The resulting solids were collected by filtration, washed with water (300 mL> 2) and dried in a vacuum oven overnight to give the title compound ( 101 g, 75percent) as a pale yellow solid. NMR (400 MHz, DMSO-ay δ 9.07 (s, 1 H), 8.47 (d, = 5.6 Hz, 1 H), 7.80 (d, J = 5.2 Hz, 1 H), 7.61 (s, 1 H). MS (ESI+) m. z: 1 64 [M+H] \
75%
With water; potassium hydroxide In tetrahydrofuran; methanol at 20℃; for 16 h;
Step 6. To a solution of ethyl furo[2,3-c]pyridine-2-carboxylate (158 g, 0.83 mol) in water:THF:MeOH (1:1:1, 2.4 L) was added KOH (139 g, 2.49 mol). Thereaction mixture was stirred at rt for 16 h and then concentrated to a volume of 750 mL. To this residue was added acetic acid until pH 4. The resulting solids were collected by filtration, washed with water (300 mLx2) and dried in a vacuum oven overnight to give the title compound (101 g, 75percent) as a pale yellow solid. 1H NMR (400 MHz, DMSO-d6) 6 9.07 (s, 1H), 8,47 (d, J 5.6 Hz, 1H), 7.80 (d, J = 5.2 Hz,1H), 7.61 (s, 1H). MS (ESI+) m/z: 164 [M+F]+
75%
With water; potassium hydroxide In tetrahydrofuran; methanol at 20℃; for 16 h;
Intermediate 1: Furo[2,3-clpyridine-2-carboxylic acid [0171] Step 6. To a solution of ethyl furo[2,3-c]pyridine-2-carboxylate (158 g, 0.83 mol) in water:THF:MeOH (1:1:1, 2.4 L) was added KOH (139 g, 2.49 mol). The reaction mixture was stirred at rt for 16 h and then concentrated to a volume of 750 mL. To this residue was added acetic acid until pH 4. The resulting solids were collected by filtration, washed withwater (300 mLx2) and dried in a vacuum oven overnight to give the title compound (101 g, 75percent) as a pale yellow solid. ‘H NMR (400 MHz, DMSO-d6) ? 9.07 (s, 1H), 8.47 (d, J = 5.6 Hz, 1H), 7.80 (d, J = 5.2 Hz, 1H), 7.61 (s, 1H). MS (ESI+) m/z: 164 [M+Hf’.
75%
With water; potassium hydroxide In tetrahydrofuran; methanol at 20℃; for 16 h;
Step 6. To a solution of ethyl furo[2,3-c]pyridine-2-carboxylate (158 g, 0.83 mol) in water:THF:MeOH (1 : 1 : 1, 2.4 L) was added KOH (139 g, 2.49 mol). The reaction mixture was stirred at rt for 16 h and then concentrated to a volume of 750 mL. To this residue was added acetic acid until pH ~ 4. The resulting solids were collected by filtration, washed with water (300 mLx2) and dried in a vacuum oven overnight to give the title compound (101 g, 75percent) as a pale yellow solid. 1H NMR (400 MHz, DMSO-J6) δ 9.07 (s, 1H), 8.47 (d, J = 5.6 Hz, 1H), 7.80 (d, J = 5.2 Hz, 1H), 7.61 (s, 1H). MS (ESI+) m/z: 164 [M+H]+.
With potassium dihydrogenphosphate; NaClO2 In tetrahydrofuran; water; <i>tert</i>-butyl alcohol
C33 (558 mg, 3.79 mmol) is dissolved in 25 mL THF, 12 mL t-butanol, and 12 mL water. KH2PO4 (1.03 g, 7.6 mmol) and NaClO2 (1.28 g, 114 mmol) are added, and the reaction is stirred 3 h at rt. The reaction is concentrated in vacuo to a residue. Water (20 mL) is added, and the pH of the mixture is adjusted to 3 with 10percent aqueous HCl. The mixture is stirred 20 min in an ice bath, the resultant white solid is collected, washed with water and dried to afford furo[2,3-c]pyridine-2-carboxylic acid (C34) (84percent yield). HRMS (FAB) calculated for C8H5NO3+H: 164.0348, found 164.0344 (M+H)+.
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