* All experimental methods are cited from the reference, please refer to the original source for details. We do not guarantee the accuracy of the content in the reference.
With hydrogenchloride; water In ethanol at 20℃; for 15 h;
10286] The resulting ethyl 1 -acetyl-1 H-indazole-5-car- boxylate was stirred in a mixture of concentrated hydrochloric acid (15 ml), water (15 ml) and ethanol (30 ml) forhours at a room temperature. The resulting mixture was rendered faintly alkaline with a 25percent ammonia water. The faintly alkalified mixture was subjected to extraction with chloroform. The extract was crystallized from n-hexane, and then the resulting crystal was separated by filtration and driedgive the title compound (6.45 g, 48percent) as a light-brown powder.
Reference：
[1] Journal of Medicinal Chemistry, 2000, vol. 43, # 1, p. 41 - 58
[2] Patent: US2013/79306, 2013, A1, . Location in patent: Paragraph 0286
2
[ 40800-65-5 ]
[ 108-24-7 ]
[ 192944-51-7 ]
[ 192944-50-6 ]
Yield
Reaction Conditions
Operation in experiment
31%
Stage #1: With potassium acetate In chloroform for 1 h; Stage #2: With 18-crown-6 ether; isopentyl nitrite In chloroform for 21 h; Reflux
Step 4-1-2 Ethyl 1H-indazole-5-carboxylate Ethyl 4-amino-3-methylbenzoate (12.6 g, 70.0 mmol) prepared in the Step 4-1-1 and potassium acetate (7.20 g, 73.5 mmol) were suspended in chloroform (70 ml). Acetic anhydride (14.3 g, 140 mmol) was added to the suspension, and the mixture was stirred for one hour. To the mixture, 18-crown-6 (3.70 g, 14.0 mmol) and isoamyl nitrite (18.9 g, 161 mmol) were added, and the resulting mixture was heated under reflux for 21 hours. After being allowed to cool, under an ice cooling the mixture was rendered faintly alkaline with a saturated sodium bicarbonate solution and a 25percent ammonia water. The faintly alkalified mixture was subjected to extraction with chloroform, and the extract was dried over anhydrous magnesium sulfate and then concentrated. The concentrate was purified by silica gel column chromatography (n-hexane:ethyl acetate=1:1) to give the title compound (4.06 g, 31percent) as a light-brown powder and ethyl 1-acetyl-1H-indazole-5-carboxylate. The resulting ethyl 1-acetyl-1H-indazole-5-carboxylate was stirred in a mixture of concentrated hydrochloric acid (15 ml), water (15 ml) and ethanol (30 ml) for 15 hours at a room temperature.
Step 4-1-2 Ethyl 1H-indazole-5-carboxylate Ethyl 4-amino-3-methylbenzoate (12.6 g, 70.0 mmol) prepared in the Step 4-1-1 and potassium acetate (7.20 g, 73.5 mmol) were suspended in chloroform (70 ml). Acetic anhydride (14.3 g, 140 mmol) was added to the suspension, and the mixture was stirred for one hour. To the mixture, 18-crown-6 (3.70 g, 14.0 mmol) and isoamyl nitrite (18.9 g, 161 mmol) were added, and the resulting mixture was heated under reflux for 21 hours. After being allowed to cool, under an ice cooling the mixture was rendered faintly alkaline with a saturated sodium bicarbonate solution and a 25% ammonia water. The faintly alkalified mixture was subjected to extraction with chloroform, and the extract was dried over anhydrous magnesium sulfate and then concentrated. The concentrate was purified by silica gel column chromatography (n-hexane:ethyl acetate=1:1) to give the title compound (4.06 g, 31%) as a light-brown powder and ethyl 1-acetyl-1H-indazole-5-carboxylate. The resulting ethyl 1-acetyl-1H-indazole-5-carboxylate was stirred in a mixture of concentrated hydrochloric acid (15 ml), water (15 ml) and ethanol (30 ml) for 15 hours at a room temperature.
Multi-step reaction with 3 steps
1.1: hydrogenchloride; water / ethanol / 15 h / 20 °C
2.1: sodium hydride / tetrahydrofuran; mineral oil / 0.17 h
2.2: 20 °C
3.1: lithium aluminium tetrahydride / tetrahydrofuran / 0.5 h / Cooling with ice
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