In a three-necked flask equipped with a stirrer, condenser tube and thermometer, add 2.4 g of m-hydroxybenzaldehyde dissolved in 40 mL of formic acid with stirring. The temperature was controlled to be below 60 °C and 4.2 g of hexahydropyridine was slowly added dropwise. After the dropwise addition was completed, the temperature was raised to 110 °C and the reaction was refluxed for 2 h (the progress of the reaction was monitored by thin layer chromatography). Upon completion of the reaction, the reaction solution was diluted with 150 mL of water and cooled to 15 °C. Decolorization was carried out by adding 0.1 g of activated carbon and filtered. The pH of the filtrate was adjusted with 12% ammonia to 8.5. allowed to stand and crystallized at 10 °C. The crystals were collected by filtration, washed with cold water and dried to give Intermediate III-1 (3-(1-piperidinylmethyl)phenol) 3.0 g as yellow crystals in 78% yield.
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