Hydrochloric Acid → 3-(2,5-Dimethyl-phenyl)-4-hydroxy-5-(1-methoxy-piperidin-4-ylmethyl)-1,5-dihydro-pyrrol-2-one

Under nitrogen, t-BuOK (1.8 g, 16.0 mmol) was added to a stirred solution of 2-[2-(2,5-dimethyl-phenyl)-acetylamino]-3-(1-methoxy-piperidin-4-yl)-propionic acid methyl ester (2.6 g, 8.0 mmol) in 15 ml of THF at 60° C. and the mixture was stirred at the same temperature for another 30 min. Then, the mixture was poured into diluted hydrochloric acid (50 ml) and extracted with ethyl acetate five times. The combined organic layers were dried over sodium sulfate, filtered and concentrated in vacuum. The residue was purified by flash chromatography on silica gel. Yield: 500 mg of 3-(2,5-dimethyl-phenyl)-4-hydroxy-5-(1-methoxy-piperidin-4-ylmethyl)-1,5-dihydro-pyrrol-2-one (compound P2.2) as a solid, mp 116-119° C.