Methanol → 3-(Methoxycarbonyl)pyrazine-2-carboxylic acid

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To a mixture of pyrazine-2,3-dicarboxylic acid (20 g, 119 mmol, 1 equiv.) was added MeOH (80 mL) followed by dropwise addition of concentrated H2SO4 (36 mL, 680 mmol, 5.7 equiv.) over 45 minutes. This method is similar to that that cited for a different substrate (J. Am. Chem. Soc., 73, 1951, 5614-5616). The reaction was heated at 75° C. for 16 hours and then cooled and quenched with water (200 mL). It was extracted with EtOAc (4×60 mL) and the organic layer washed several times with water (3×50 ml), saturated NaHCO3 (50 ml), brine solution (50 mL). It was dried over Na2SO4, filtered and concentrated in vacuo to yield pyrazine-2,3-dicarboxylic acid methyl ester 241 as a brown solid (47%, 10.97 g, 55.9 mmol). 1H NMR (300 MHz) CDCl3 δ 8.79 (d, J=2.7 Hz, 2 H), 4.05 (s, 3 H), 4.04 (s, 3 H). TLC Rf: 0.7 ethyl acetate/methanol (9/1)

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