Dimethylformamide → 3-Tert-butoxy-5-chloropyrazine-2-carboxaldehyde

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After dissolving 11.4 ml of 2,2,6,6-tetramethylpiperidine in 100 ml of tetrahydrofuran, the solution was cooled to −30° C. Next, 24.1 ml of n-butyllithium (2.6 M, n-hexane solution) was added dropwise under a nitrogen atmosphere. After stirring for 5 minutes, the mixture was cooled on ice and stirred for an additional 20 minutes. It was then cooled to −78° C., and a solution of 9.00 g of 2-tert-butoxy-6-chloropyrazine in tetrahydrofuran (10 ml) was added dropwise at below −70° C. The mixture was then stirred for 30 minutes, and 6 ml of N,N-dimethylformamide was added dropwise at below −65° C. After 10 minutes, 50 ml of toluene was added to the reaction solution at below −60° C., and after 2 minutes, a tetrahydrofuran solution (5 ml) containing 2 ml of water was added at below −65° C. After an additional 5 minutes, 60 ml of 50% aqueous acetic acid was added at once, and after 5 minutes, 100 ml of water was added and the temperature was raised to room temperature. The reaction solution was extracted with ethyl acetate, washed with water, a 1N sodium hydroxide solution, water and saturated brine in that order, and dried over anhydrous magnesium sulfate. The solvent was distilled off under reduced pressure to obtain 9.39 g of crude 3-tert-butoxy-5-chloropyrazine-2-carboxaldehyde.

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