[F:1][C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][C:3]=1[C@@:8]1([CH3:21])[N:17]=[C:16]([NH2:18])[C:11]2([CH2:15][CH2:14][CH2:13][CH2:12]2)[S:10](=[O:20])(=[O:19])[CH2:9]1.S(=O)(=O)(O)O.[N+:27]([O-])([OH:29])=[O:28].[OH-].[Na+]>>[F:1][C:2]1[CH:7]=[CH:6][C:5]([N+:27]([O-:29])=[O:28])=[CH:4][C:3]=1[C@@:8]1([CH3:21])[N:17]=[C:16]([NH2:18])[C:11]2([CH2:12][CH2:13][CH2:14][CH2:15]2)[S:10](=[O:20])(=[O:19])[CH2:9]1(R)-8-(2-Fluoro-phenyl)-8-methyl-6,6-dioxo-6λ6-thia-9-aza-spiro[4.5]dec-9-en-10-ylamine (172 mg, 554 μmol, Eq: 1.00) was dissolved in conc. sulfuric acid (2.72 g, 1.48 ml, 27.7 mmol, Eq: 50), then at 0° C. fuming nitric acid (52.4 mg, 37.1 μl, 831 μmol, Eq: 1.5) was added dropwise. The light brown solution was stirred at 0° C. for 2 hours. The reaction mixture was poured on ice and basified with 3 N NaOH followed by extraction with dichloromethane. The organic layer was separated, dried over Na2SO4, filtered and evaporated to dryness to give the crude and pure (R)-8-(2-fluoro-5-nitro-phenyl)-8-methyl-6,6-dioxo-6λ6-thia-9-aza-spiro[4.5]dec-9-en-10-ylamine (210 mg, 591 μmol, 107% yield) as an off-white foam. MS (ISP): m/z=356.5 [M+H]+.
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