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With iodine; potassium hydroxide; In N,N-dimethyl-formamide; at 0 - 20℃; for 3.0h;
To a solution of Scheme 9-1 compound SI (1 equiv) in DMF (20 vol) at 0 C is added iodine (1.5 equiv) and potassium hydroxide (2.5 equiv). The reaction mixture is stirred at room temperature for 3 h and then quenched with 10% aqueous sodium thiosulfate solution. The resulting mixture is extracted with ethyl acetate. The organic layer is separated, dried over anhydrous Na2S04, filtered and then concentrated. The residue is purified by column chromatography on silica gel to afford Scheme 9-1 compound S2
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.
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