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Stage #1: at -20℃; for 0.5 h; Stage #2: for 2 h; Reflux
Preparation 405-Hvdroxy-pyrazine-2-carboxylic acid methyl esterThionyl chloride (152ml_, 2.08mol) was added dropwise at -20 °C to methanol (5L). After the addition was completed, the mixture was stirred at this temperature for 30 minutes. Then 5- hydroxy-pyrazine-2-carboxylic acid (100g, 714mmol) was added, and the mixture was heated at reflux for 2 hours. The reaction mixture was concentrated in vacuo, and the residue was recrystallised from methanol (400ml_) to give 71 g (464mmol) of the title compound in 65percent yield.
61%
With hydrogenchloride In 1,4-dioxane; water at 60 - 80℃; for 4 h;
(62a) Methyl 5-hydroxypyrazine-2-carboxylate Commercially available 5-hydroxypyrazine-2-carboxylic acid (1.00 g, 7.14 mmol) was dissolved in methanol (5 mL), and a 4N hydrochloric acid/dioxane solution (25 mL) was added, followed by stirring at 60°C for 1.5 hours and heating to reflux at 80°C for 2.5 hours. The reaction solution was brought back to room temperature, the solvent was distilled off under reduced pressure, and ethyl acetate (20 mL) was added to the resulting residue to allow it to be suspended. The resulting precipitate was filtered off, and washed with ethyl acetate, followed by vacuum drying, to afford the desired compound (673 mg, yield 61percent) as an orange-brown solid. 1H-NMR (CD3OD, 400 MHz): δ 3.31 (1H, s), 3.85 (3H, s), 8.00 (1H, d, J=1.2 Hz), 8.13 (1H, d, J=1.2 Hz).
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