C([CH:3]([C:7]1([CH3:20])[C:15]2[C:10](=[CH:11][CH:12]=[CH:13][C:14]=2[N+:16]([O-])=O)[NH:9][C:8]1=S)[C:4]([O-:6])=[O:5])C.[BH4-].[Na+].[CH2:23]1COC[CH2:24]1>CO.O.O.O.O.O.O.[Ni](Cl)Cl>[NH2:16][C:14]1[CH:13]=[CH:12][CH:11]=[C:10]2[C:15]=1[C:7]([CH2:3][C:4]([O:6][CH2:23][CH3:24])=[O:5])([CH3:20])[CH2:8][NH:9]2To a solution of (±)-ethyl (3-methyl-4-nitro-2-thioxo-2,3-dihydro-1H-indol-3-yl)acetate from Step A (3.65 g, 12.4 mmol) and nickel (II) chloride hexahydrate (23.6 g, 99.2 mmol) in MeOH (30 mL) and THF (30 mL), at 0° C., was added NaBH4 (11.3 g, 298 mmol) in portions over 1 h. The resulting mixture was stirred for 10 min, then filtered through a pad of Celite, washing with MeOH, and the filtrate was concentrated in vacuo. The residue was purified by silica gel chromatography, eluting with CH2Cl2:MeOH—90:10, to give the title compound. MS: m/z=235 (M+1).
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