2-(cis-4-{[tert-Butyl(dimethyl)silyl]oxy}cyclohexyl)-2,7-diazaspiro[4.5]decan-1-one (7.00 g, 19.1 mmol) was dissolved in acetonitrile (50 mL) and methanol (7 mL) at r.t. After the starting material was completely dissolved, the solution was heated up to 70° C. To the above solution was slowly added a solution of (2R)-hydroxy(phenyl)acetic acid (1.45 g, 9.55 mmol) in acetonitrile (20 mL) at 65-70° C. After addition, the solution was heated at 74° C. for 10 min, and allowed to cool slowly to room temperature overnight. The crystalline formed was collected by filtration to afford 3.38 g of the desired product as (2R)-hydroxy(phenyl)acetic acid salt. The resulting salt (3.38 g) was dissolved in water (50 mL), and adjusted to pH˜12 with 40 mL aq K2CO3 solution (2.0 M). The mixture was extracted with dichloromethane (3 times). The combined organic layers were dried with magnesium sulfate, filtered, and concentrated under reduced pressure to afford the desired product as a free base (colorless crystalline solid) (2.37 g). The absolute stereochemistry of this compound was established by X-ray single crystal structure determination of (2R)-hydroxy(phenyl)acetic acid salt of (5S)-2-(cis-4-{[tert-butyl(dimethyl)silyl]oxy}cyclohexyl)-2,7-diazaspiro[4.5]decan-1-one.
