To a solution of Boc-carbamate (2.68 g, 22.9 mmol) in nPrOH (70 mL) at 25° C. was added an NaOH solution (32 mL, prepared from 900 mg of NaOH in 37 mL H2O) followed by tBuOCl (2.58 mL, 22.51 mmol). After 15 min, phenylmethyl 8-azaspiro[4.5]dec-2-ene-8-carboxylate (2 g, 7.4 mmol) in nPrOH (3 mL) was added followed by K2OsO2(OH)2 (109 mg, 0.295 mmol) dissolved in the remaining NaOH solution prepared above (5 mL). After 1 h, the solution was extracted with EtOAc, concentrated and purified via column chromatography (1-7% MeOH in DCM (1% NH4OH)) yielding the title compound (˜3.1 g, contaminated with residual Boc-carbamate) as a white solid: LCMS (ES) m/e 405 (M+H)+.
