[CH3:1][C:2]([NH2:11])([CH2:4][C:5]1[CH:6]=[CH:7][CH:8]=[CH:9][CH:10]=1)[CH3:3].S(=O)(=O)(O)O.[N+:17]([O-])([OH:19])=[O:18].O>C(Cl)(Cl)Cl>[CH3:3][C:2]([NH2:11])([CH3:1])[CH2:4][C:5]1[CH:6]=[CH:7][C:8]([N+:17]([O-:19])=[O:18])=[CH:9][CH:10]=1A solution of phentermine (1.0 g) in chloroform (20 ml) was added dropwise to sulfuric acid (3.57 ml) at 0° C.; then fuming nitric acid (specific gravity=1.52; 2.8 ml) was added dropwise at 0° C. The reaction mixture was stirred at 0° C. for 2 h, made alkaline with water and a 2 N aqueous sodium hydroxide solution and extracted with ethyl acetate. The organic layer was washed with a saturated aqueous sodium chloride solution, dried with anhydrous sodium sulfate and concentrated under reduced pressure. The resulting residue was purified by silica gel column chromatography (eluent, chloroform:methanol=9:1) to give 367 mg of the titled compound (yield, 28%).
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