A solution of 4-((1-(tert-butoxycarbonyl)-4-isocyanatopiperidin-4-yl)methyl)-1-tert-butyl-1H-pyrazole-3-carboxylic acid (180 mg, 0.44 mmol) in tetrahydrofuran (5 mL) was treated with 2 N aqueous sodium hydroxide (0.664 mL, 1.33 mmol). The mixture was stirred 3 hours at room temperature, tetrahydrofuran and water were removed on a rotary evaporator and the resultant colorless solid was slurried in acetonitrile (10 mL) and then concentrated to dryness. The trituration was repeated twice more from acetonitrile (10 mL). The resultant colorless solid was taken up in dichloromethane (10 mL) and treated with (3-(dimethylamino)propyl)ethyl carbodiimide hydrochloride (170 mg, 0.89 mmol). The mixture was stirred 18 hours at room temperature and then diluted with dichloromethane (50 mL) and washed with water (30 mL). The organic phase was dried over sodium sulfate, filtered and concentrated. The residue was then purified by flash chromatography (30-100% ethyl acetate/heptanes, 10 g silica gel) to yield tert-butyl 2′-tert-butyl-7′-oxo-2′,4′,6′,7′-tetrahydrospiro[piperidine-4,5′-pyrazolo[3,4-c]pyridine]-1-carboxylate (70 mg) as a colorless solid. +ESI (M+H) 363.3; 1H NMR (400 MHz, DMSO-d6, δ): 7.68 (s, 1H), 7.57 (s, 1H), 3.47 (m, 2H), 3.20 (m, 2H), 2.73 (s, 2H), 1.53 (t, J=5.7 Hz, 4H), 1.49 (s, 9H), 1.36 (s, 9H).
