[N+]([C:4]1[CH:5]=C(S([O-])(=O)=O)C=[CH:8][CH:9]=1)([O-])=O.[Na+].[N:15]1[C:24]2[CH:23]=[CH:22][CH:21]=[C:20]([NH2:25])[C:19]=2[CH:18]=[CH:17][CH:16]=1.C(=O)/C=C/C.[OH-].[Na+]>OS(O)(=O)=O.O=S(=O)=O.O>[CH3:8][C:9]1[CH:4]=[CH:5][C:21]2[C:20](=[C:19]3[C:24](=[CH:23][CH:22]=2)[N:15]=[CH:16][CH:17]=[CH:18]3)[N:25]=1To a mixture of sodium 3-nitrobenzenesulfonate (2.88 g, 12.8 mmol) in oleum (12 mL) and water (12 mL) was added quinolin-5-amine (3.09 g, 21.4 mmol). The mixture was stirred and heated to 105° C. Crotonaldehyde (3.00 g, 42.8 mmol) was added dropwise over 15 min. The resulting mixture was stirred at 105° C. for 16 h. The mixture was then poured into ice (50 g), and the pH value was adjusted to 11 with 1 N aqueous sodium hydroxide solution. The mixture was extracted with EtOAc (3×60 mL), and the combined organic layers were dried over anhydrous sodium sulfate and concentrated under reduced pressure. The residue was purified by column chromatography to afford 2-methyl-1,7-phenanthroline as a yellow solid (2.10 g). MS (ESI) m/z 195.1 (M+H)+.
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