495414-81-8

268550-48-7

B) Synthesis of tert-butyl 1-oxo-2,8-diazaspiro[4.5]decane-8-carboxylate 4-(Cyanomethyl)-1,4-piperidinedicarboxylic acid-1-(1,1-dimethylethyl)4-ethyl ester (2.5 g) was dissolved in methanol (50 mL), and cobalt(II) chloride hexahydrate (1.0 g) and sodium borohydride (1.6 g) were added sequentially under ice bath cooling. The reaction mixture was stirred by keeping the ice bath cool for 2 h. Subsequently, the ice bath was removed and stirring was continued for 2 h at room temperature. The reaction system was then warmed to 60°C for 1 hour. After completion of the reaction, 28% ammonia solution was added to the system and the resulting precipitate was removed by filtration. The filtrate was extracted with ethyl acetate, the organic layers were combined and dried over anhydrous magnesium sulfate. The solvent was removed by concentration under reduced pressure and the resulting crude product was purified by silica gel column chromatography (eluent: ethyl acetate) to afford the target compound tert-butyl 1-oxo-2,8-diazaspiro[4.5]decane-8-carboxylate (1.1 g). The product was characterized by 1H NMR (300 MHz, DMSO-d6): δ 1.25-1.35 (2H, m), 1.40 (9H, s), 1.45-1.58 (2H, m), 1.90-1.98 (2H, m), 2.90 (2H, brs), 3.16 (2H, t, J=7.2Hz), 3.76-3.86 ( 2H, m), 7.56 (1H, brs).