[CH3:1][CH:2]1[N:7]([C:8]2[CH:13]=[CH:12][C:11](N)=[CH:10][CH:9]=2)[CH2:6][CH2:5][N:4]([C:15]([O:17][C:18]([CH3:21])([CH3:20])[CH3:19])=[O:16])[CH2:3]1.N([O-])=O.[Na+].[OH-].[Na+]>[PH2](O)=O.O.[Cu-]=O>[CH3:1][CH:2]1[N:7]([C:8]2[CH:13]=[CH:12][CH:11]=[CH:10][CH:9]=2)[CH2:6][CH2:5][N:4]([C:15]([O:17][C:18]([CH3:19])([CH3:21])[CH3:20])=[O:16])[CH2:3]1To a solution of (±)-tert-butyl 3-methyl-4-(4-aminophenyl)piperazine-1-carboxylate (325 mg) in 50% hypophosphorous acid (1.27 ml) containing copper(I) oxide (8.0 mg) was added dropwise a solution of sodium nitrite (92 mg) in water (2 ml) at 0° C. with stirring. After 2 hours, the reaction mixture was made alkaline with 40% NaOH solution and extracted with ethyl acetate twice. The organic layers were combined and washed with water and brine. The solvent was evaporated, and the residue was purified by silica gel column chromatography (hexane-ethyl acetate 1:1) to give the title compound in a pure form as colorless oil.
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