Acetonitrile (144 mL) and water (336 mL) were added to a mixture of 4-(3,4-dichloro-2-methyl-phenoxy)-piperidine hydrochloride (60 g), 4-(toluene-4-sulfonyloxymethyl)-piperidine-1-carboxylic acid tert-butyl ester (74.7 g) and potassium carbonate (57.3 g) and the mixture was heated to reflux for 7 h, then cooled over 30 min to 75° C. and held at 75° C. for 14 h, then heated over 30 min to reflux. Acetonitrile (192 mL) was added and then the mixture was cooled to 20° C. over 2 h to give a suspension. The suspension was filtered under vacuum, the filter cake was washed with water (180 mL) and then with acetonitrile (180 mL) and dried under vacuum at 40° C. to give 4-[4-(3,4-dichloro-2-methyl-phenoxy)-piperidin-1-ylmethyl]-piperidine-1-carboxylic acid tert-butyl ester as a white solid (73.9 g).
