50 ml of 2-methyltetrahydrofuran are distilled off from the solution consisting of 9.15 g (28.29 mmol, 1.0 eq) 2-amino-N-[1-(phenylmethyl)-4-piperidinyl]-phenylacetamide in 162 ml of 2-methyltetrahydrofuran. The solution is cooled to −12° C. and 4.56 g (45.10 mmol, 1.6 eq) 4-methylmorpholine are added, followed by 4.26 g (45.10 mmol, 1.6 eq) methyl chloroformate. The reaction mixture is stirred for another 1 hour at 20° C. and then combined with 100 ml of water. After phase separation the aqueous phase is washed with 20 ml 2-methyltetrahydrofuran and the combined organic phases are washed with 50 ml of water. The organic solvent is distilled off in vacuo. The residue is combined with 50 ml of acetone and refluxed. Then 100 ml of water are added and the suspension obtained is cooled to 20° C. To complete the crystallisation the mixture is stirred for 30 minutes at 20° C. Then the product is suction filtered, washed with 30 ml acetone-water mixture (1:2) and dried in the dryer at 45° C. while being rendered inert.
