[NH2:1][C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][N:3]=1.[CH:8](=O)[CH2:9][CH2:10][CH3:11].C(O[BH-](OC(=O)C)OC(=O)C)(=O)C.[Na+].C(OCC)(=O)C>C(Cl)(Cl)Cl.C(O)(=O)C>[CH2:8]([NH:1][C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][N:3]=1)[CH2:9][CH2:10][CH3:11]2-aminopyridine (5.0 g) was dissolved in chloroform (40 mL) and acetic acid (10 mL), and n-butyraldehyde (4.2 g) was added, then stirred at room temperature for 30 minutes. Sodium triacetoxyborohydride (16.9 g) was added and stirred at room temperature for three hours. Ethyl acetate (300 mL) was added to the reaction solution, and the organic layer was washed with saturated aqueous solution of sodium hydrogen carbonate (200 mL) and saturated sodium chloride solution (50 mL). After drying on anhydrous sodium sulfate, filtration, and vacuum concentration, the residue was purified by silica gel flash column chromatography (developing solvent: n-hexane:ethyl acetate=2:1) to give the above-identified compound (2.7 g, yield 34%).
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