(R)-tert-butyl 3-((R)-(2-amino-2-oxoethoxy)(3-chlorophenyl)methyl)piperidine-1-carboxylate (1.10 g, 2.60 mmol) was dissolved in anhydrous toluene (30 mL) and cooled to 0° C. Red-Al (65% in toluene, 2.6 mL, 8.64 mmol) was added dropwise. After the addition, the reaction was stirred at rt for 12 h and quenched by adding water slowly. The resulting mixture was filtered through Celite and washing with THF. The filtrate was evaporated under reduced pressure to give crude product 1.05 g. It was used for next step without further purification.
