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4,7-Dichloroquinoline (20.4 g) and peracetic acid (32 wt. % [from Aldrich], 24 mL) are heated at reflux for 8 h and kept at room temp. for 18 h. The precipitate is collected and washed with hexane to give 23 g of 4,7-dichloroquinoline-N-oxide. 1.0 g (4.7 mmol) thereof is heated in phosphoryl chloride (3.7 mL) for 1½ h at reflux. The reaction mixture is concentrated and the residue is treated with 10% aq. NaOH (pH 9). The precipitate is collected, washed with water, and dried yielding 1.0 g of 2,4,7-trichloroquinoline. 250 mg thereof is heated with 15% H2SO4 (20 mL) and 1,4-dioxane (10 mL) in a sealed tube at 140° C. for 8 h. The mixture is kept at room temp. for 18 h. The precipitate is collected, washed with water, and dried affording 195 mg of 4,7-dichloro-2-quinolone.

1. temperatureat reflux for 8 h
2. customThe precipitate is collected
3. washwashed with hexane