[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][N:11]([CH2:14][C:15]2[CH:20]=[CH:19][C:18]([N+:21]([O-])=O)=[CH:17][CH:16]=2)[CH2:10][CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].O.O.[Sn](Cl)(Cl)(Cl)Cl.C(=O)(O)[O-].[Na+]>C(OCC)(=O)C>[C:1]([O:5][C:6]([N:8]1[CH2:9][CH2:10][N:11]([CH2:14][C:15]2[CH:16]=[CH:17][C:18]([NH2:21])=[CH:19][CH:20]=2)[CH2:12][CH2:13]1)=[O:7])([CH3:4])([CH3:2])[CH3:3]4-(4-Nitro-benzyl)-piperazin-1-yl carboxylic acid tert-butyl ester (769 mg, 2.4 mmol) and tin chloride dihydrate (2.70 g, 12 mmol) are suspended in ethyl acetate (20 mL) and stirred at room temperature overnight. Then, saturated aqueous solution of sodium bicarbonate (20 mL) is added and vigorously stirred for 1 hour. Solids are removed by filtration and the organic layer of the filtrate is separated and washed with water (20 mL). The organic phase is dried over anhydrous magnesium sulfate and concentrated to give a white solid (620 mg, 89% yield, ES+(m/z) 293 [M+H]).
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