5.00 g (13.11 mmol, 1.0 eq) 2-methoxycarbonylamino-N-[1-(phenylmethyl)-4-piperidinyl]-phenylacetamide from Example 3 are suspended in 50 ml of toluene and heated to 80° C. At this temperature 56.1 g (78.61 mmol, 6.0 eq) diisobutylaluminium hydride in toluene (20%) are metered in. After the addition has ended the reaction mixture is stirred for another 30 minutes at this temperature. After cooling to 10° C. the mixture is adjusted to pH=2.5 with hydrochloric acid. The precipitate formed is dissolved with sodium hydroxide solution and after phase separation the organic phase is washed with 50 ml of water. The organic phase is evaporated down in vacuo to an oil and combined with 50 ml of methanol.
