Sodium sulfate decahydrate → 1-Methyl-1,2,3,6-tetrahydropyridine-4-carboaldehyde

To a solution prepared by dissolving 1.7 g of ethyl 1-methyl-1,2,3,6-tetrahydro-4-pyridinecarboxylate in 20 mL of tetrahydrofuran, 773 mg of lithium aluminum hydride was added, and the mixture was stirred for 1 hour at room temperature. The reaction solution was cooled to 0° C., and then sodium sulfate decahydrate was slowly added until there are no bubbles, and stirred overnight at room temperature. The insolubles were filtered and the filtrate was concentrated under reduced pressure. The obtained residue was dissolved in 40 mL of chloroform, then 2 g of manganese dioxide was added thereto, and the mixture was stirred overnight at room temperature. The insolubles were filtered through celite, the filtrate was concentrated under reduced pressure, and the resulting residue was purified by silica gel column chromatography (eluent: chloroform/methanol=100/0-90/10), to obtain 212 mg of 1-methyl-1,2,3,6-tetrahydropyridine-4-carboaldehyde [34-1] (hereinafter, referred to as the compound [34-1]).