In a mixture of 120 ml of ethyl acetate and 13 g of pyridine is dissolved 12.8 g of ethyl 6-(1-benzyloxycarbonyl-4-piperidyl)-2-hydroxyhexanoate, and 5.1 ml of thionyl chloride is added to the solution, followed by refluxing with stirring for 45 minutes. After cooling, 500 ml of water and 200 ml of ethyl acetate are added to the reaction solution, and extraction is carried out. The extract is washed with 0.1N hydrochloric acid and water successively, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The resulting oily material is purified by silica gel column chromatography (hexane:ethyl acetate=4:1) to give 10 g of ethyl 6-(1-benzyloxycarbonyl-4-piperidyl)-2-chlorohexanoate as a colorless oily material.
