To a mixture of ethyl 6-(1-benzyloxycarbonyl-4-piperidyl)-2-hydroxyhexanoate (12.8 g), ethyl acetate (120 ml) and pyridine (13 g) is added thionyl chloride (5.1 ml). The mixture is refluxed for 45 minutes with stirring. After cooling, the mixture is diluted with water (500 ml) and extracted with ethyl acetate (200 ml). The extract is washed successively with 0.1N hydrochloric acid and water, dried over anhydrous magnesium sulfate and concentrated in vacuo. The oily residue is chromatographed on silica gel using hexane-ethyl acetate (4:1) as an eluent to yield ethyl 6-(1-benzyloxycarbonyl-4-piperidyl)-2-chlorohexanoate (10 g) as a colorless oil.
