1242268-17-2

871727-05-8

Step 3: 6-tert-butyl 1-ethyl 6-azaspiro[2.5]octane-1,6-dicarboxylate (500 mg, 1.76 mmol) was dissolved in ethanol (8 mL) and a solution of sodium hydroxide (212 mg, 5.3 mmol) in water (4 mL) was added. The reaction mixture was stirred at 15°C for 12 hours. After completion of the reaction, the solvent was removed by evaporation under reduced pressure. The residue was dissolved in water and slowly acidified with dilute hydrochloric acid (0.5 M) under cooling in an ice bath to pH ~ 4. The aqueous phase was extracted with ethyl acetate (10 mL x 3). The organic phases were combined, dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure to give 6-(tert-butoxycarbonyl)-6-azaspiro[2.5]octane-1-carboxylic acid (390 mg, 83% yield) as a white solid.1H NMR (400 MHz, CDCl3): δ 3.52-3.42 (m, 3H), 3.38-3.35 (m, 1H), 1.75- 1.72 (m, 2H), 1.58-1.56 (m, 1H), 1.46-1.43 (m, 11H), 1.23-1.21 (m, 1H), 1.02-1.01 (m, 1H).