[O:1]=[C:2]1[C:6]2([CH2:11][CH2:10][N:9]([C:12]([O:14][C:15]([CH3:18])([CH3:17])[CH3:16])=[O:13])[CH2:8][CH2:7]2)[CH2:5][CH2:4][N:3]1[C:19]1[CH2:20][O:21][C:22](=[O:26])[C:23]=1[CH:24]=C.I([O-])(=O)(=O)=[O:28].[Na+]>CC(C)=O.O>[CH:24]([C:23]1[C:22](=[O:26])[O:21][CH2:20][C:19]=1[N:3]1[CH2:4][CH2:5][C:6]2([CH2:7][CH2:8][N:9]([C:12]([O:14][C:15]([CH3:18])([CH3:17])[CH3:16])=[O:13])[CH2:10][CH2:11]2)[C:2]1=[O:1])=[O:28]tert-butyl 1-oxo-2-(5-oxo-4-vinyl-2,5-dihydrofuran-3-yl)-2,8-diazaspiro[4.5]decane-8-carboxylate (1.6 g, 4.4 mmol) was dissolved in acetone (36 mL) and water (36 mL), then K2OsO4.2H2O was added and the mixture was stirred for ˜5 min. Solid sodium periodate (3.77 g, 17.6 mmol) was added in 4 portions during 1 hour and the reaction temperature was maintained below 40° C. using an ice-bath. The resulting mixture was stirred for 1 hour at room temperature. LCMS after 2 hours showed complete consumption of starting material. The suspension was filtered and the filtrate was concentrated to remove acetone. The aqueous layer was extracted with DCM (3×). Combined organic layers were washed with 10% Na2S2O3 solution (2×), dried over anhydrous Na2SO4, filtered, concentrated to obtain the title compound, which was taken to the next step without further purification.
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