Methylglyoxal → 1-ethyl-5-methylpyrazin-2(1H)-one

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A cold (0° C.) solution of N2-tert-butoxycarbonyl-N1-ethylglycinamide (68.0 g, 0.33 mol) in anhydrous dichloromethane (500 mL) was saturated with anhydrous hydrogen chloride gas. After stirring at the same temperature for 1.5 hours, the solution was recharged with more hydrogen chloride gas and stirred for additional 15 minutes. The reaction mixture was concentrated under vacuum. The residue was dissolved in methanol, diluted with toluene, and concentrated under vacuum to afford the intermediate N-ethylglycinamide HCl salt. This was stored under vacuum overnight and used without further purification. A solution of N-ethylglycinamide HCl salt (44.2 g, 0.32 mol), aqueous sodium hydroxide (640 mL, 1M), water (350 mL), pyruvic aldehyde (20.9 mL, 40% solution in water) was heated in an oil bath at 120° C. for one hour. The reaction mixture was cooled and saturated with solid sodium chloride. The mixture was extracted with chloroform (4×250 mL). The combined organic extract was dried over anhydrous sodium sulfate, filtered, and passed through a plug of silica gel. The silica gel was rinsed successively with ethyl acetate and then 2% methanol in ethyl acetate. The eluted fractions were combined and concentrated under vacuum. The residual solid was recrystallized from diethyl ether to afford the title compound as pale yellow solid.

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