| 90% |
With sodium t-butanolate In toluene at 105℃; for 6 h; |
30 mol of methyl 4-benzyloxy-2-((dimethylamino)methylene)-3-acetoacetate obtained in Example 2 and 45 mol of dimethyl oxalate,15 mol of sodium t-butoxide and 300 ml of toluene were placed in a reaction flask, and then the reaction flask was placed in an oil bath, heated to 105 ° C, refluxed for 6 h, after completion of the reaction, cooled to room temperature, and filtered.The toluene solvent was removed by rotary evaporation, followed by separation of the crude product by column chromatography, eluent: n-hexane: ethyl acetate = 9:4.Thus obtaining dimethyl 4-oxo-3-benzyloxy-4H-pyran-2,5-dicarboxylate in a yield of 90percent; |
| 85% |
Stage #1: With sodium t-butanolate In 1,3-dimethyl-2-imidazolidinone at 20 - 30℃; for 7 h; Inert atmosphere
Stage #2: With hydrogenchloride In 1,3-dimethyl-2-imidazolidinone; water at 20℃; for 15 h; |
Third StepSodium tert-butoxide (2.55 g, 23.2 mmol), dimethyl oxalate (639 mg, 5.41 mmol) and DMI (3 ml) were added to a three-neck flask under a nitrogen atmosphere, and a solution of Compound 1C (0.50 g, 1.80 mmol) in DMI (2 ml) was added dropwise thereto at 25 to 30° C. After stirring at room temperature for 7 hours, 2N hydrochloric acid (10 ml) was added, and the mixture was stirred at room temperature for 15 hours. The reaction solution was extracted with ethyl acetate two times, and the combined extracts were washed sequentially with water, saturated sodium bicarbonate water, water and saturated sodium chloride water, and then dried with anhydrous sodium sulfate. The solvent was distilled off, and the resulting residue was purified by silica gel column chromatography (n-hexane-ethyl acetate 2:1 to 1:1, v/v) to obtain 488 mg (yield 85percent) of Compound 1D as a white crystal.1H-NMR (CDCl3) δ: 3.89 (3H, s), 3.93 (3H, s), 5.34 (2H, s), 7.32-7.40 (3H, m), 7.45-7.49 (2H, m), 8.50 (1H, s). |
| 85% |
Stage #1: at 25 - 30℃; for 7 h; Inert atmosphere
Stage #2: at 20℃; for 15 h; |
Sodium tert-butoxide (2.55 g, 23.2 mmol), dimethyl oxalate (639 mg, 5.41 mmol), and DMI (3 ml) were added to a three-neck flask in a nitrogen atmosphere, and a DMI (2 ml) solution of compound 1C (0.50 g, 1.80 mmol) was added dropwise thereto at 25-30°C. After stirring at room temperature for 7 hours, 2 N hydrochloric acid (10 ml) was added thereto, and the mixture was stirred at room temperature for 15 hours. After extraction two times with ethyl acetate, the combined extracts were washed with water, a saturated aqueous solution of sodium bicarbonate, water, and saturated saline in this order and then dried over anhydrous sodium sulfate. The solvent was distilled off, and the obtained residue was purified by silica gel column chromatography (n-hexane-ethyl acetate: 2:1 1 → 1:1, v/v) to obtain 488 mg (yield: 85percent) of compound 1D as white crystals. 1H-NMR (CDCl3) δ: 3.89 (3H, s), 3.93 (3H, s), 5.34 (2H, s), 7.32-7.40 (3H, m), 7.45-7.49 (2H, m), 8.50 (1H, s). |
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