To a refluxing suspension of (±)-2′-oxo-1′,2′,5,7-tetrahydrospiro[cyclopenta[c]pyridine-6,3′-pyrrolo[2,3-b]pyridine]-3-carboxylic acid (200 mg, 0.711 mmol, described in Intermediate 5) and triethylamine (0.149 mL, 1.07 mmol) in tert-butanol (10 mL) was added diphenylphosphoryl azide (0.184 mL, 0.853 mmol). After 18 h at reflux, the mixture was concentrated in vacuo. The residue was partitioned between CH2Cl2 (50 mL) and saturated NaHCO3 (30 mL) The organic layer was separated and the aqueous layer was further extracted with CH2Cl2 (2×50 mL). The combined organic layers were dried over Na2SO4, filtered, and concentrated in vacuo. The crude product was purified by silica gel chromatography, eluting with a gradient of CH2Cl2:MeOH: NH4OH-100:0:0 to 95:5:1, to give the title compound. MS: m/z=353 (M+1).
