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The general procedure for the synthesis of tert-butyl 2-hydroxy-6-azaspiro[3.4]octane-6-carboxylate using 6-Boc-2-oxo-6-azaspiro[3.4]octane as starting material was as follows: to a solution of 6-Boc-2-oxo-6-azaspiro[3.4]octane (19 g, 84.3 mmol) in tetrahydrofuran (THF, 200 mL) at 0 °C, slowly sodium borohydride (NaBH4, 12.8 g, 337.2 mmol) was added. After addition, the reaction mixture was gradually warmed up to ambient temperature and stirred continuously for 6 hours. Upon completion of the reaction, the reaction was quenched with methanol (MeOH) and water (H2O), followed by extraction with ethyl acetate (EtOAc). The organic layers were combined, washed with saturated saline (brine), dried over anhydrous sodium sulfate (Na2SO4) and concentrated under reduced pressure. The crude product was purified by fast column chromatography (silica gel (SiO2) as stationary phase and petroleum ether solution of petroleum ether (Hep) to 50% ethyl acetate (EtOAc) as eluent) to afford the target product tert-butyl 2-hydroxy-6-azaspiro[3.4]octane-6-carboxylate (R-6, 12 g, 63% yield).

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