[N+:1]([C:4]1[CH:9]=[CH:8][C:7]([S:10]([N:13]2[CH2:18][CH2:17][CH2:16][CH2:15][CH2:14]2)(=[O:12])=[O:11])=[CH:6][CH:5]=1)([O-])=O.[Cl-].[NH4+].C(O)C.NO>[Fe].O>[N:13]1([S:10]([C:7]2[CH:6]=[CH:5][C:4]([NH2:1])=[CH:9][CH:8]=2)(=[O:12])=[O:11])[CH2:14][CH2:15][CH2:16][CH2:17][CH2:18]1
1-(4-Nitro-benzenesulfonyl)-piperidine (30 g) was mixed with iron powder (50 g), ammonium chloride (50 g), ethanol (200 ml) and water (50 ml). The mixture was heated under reflux conditions for 2 h. LCMS showed that the reduction goes through a hydroxylamine intermediate. The mixture was filtered through Celite while hot and the iron residues washed with warm ethanol, ethyl acetate, water and dichloromethane. All volatiles were removed under reduced pressure and the residue partitioned between water and ethyl acetate. The organic solution was separated and washed with brine, dried over MgSO4 concentrated to give 4-(piperidine-1-sulfonyl)-phenylamine, 23 g. 1H NMR CDCl3 7.43 (2H, d), 6.67 (2H, d), 3.33 (2H, bs), 2.84 (4H, t), 1.53 (4H, m), 1.31 (2H, m)
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