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With phosphorus tribromide In N,N-dimethyl-formamide at 45 - 60℃; for 0.75 h;
To a solution of intermediate A.i (20 g, 122.58 mmol) in DMF (130 niL), heated to 600C, was added phosphorous tribromide (13 mL, 1.15 eq.). The reaction was heated at 45°C for 45 min. After cooling to rt, the reaction was diluted with water (200 mL). Sat. Na2CO3 was added until pH 10 was reached. The solid was formed was filtered off. The solid was taken up in EA (200 mL) and the solution was concentrated to dryness. The residue was chromatographed (EA) to afford the title bromide as a yellowish solid (22 g, 79percent yield). 1H NMR (CDCl3) δ: 8.70 (d, J = 4.7 Hz, IH); 8.14 (m, IH); 7.96 (d, J = 4.7 Hz, IH); 7.81-7.73 (m, 2H).
(b) 4-Chloro-6-fluoroquinoline A mixture of 52 g (0.319 mol) of <strong>[391-78-6]6-fluoro-4-hydroxyquinoline</strong> and 100 ml of phosphorus oxychloride was stirred and heated under reflux for 3 hr. The reaction mixture was concentrated in vacuo. A slurry of the residue in methylene chloride was poured into ice-water, and the mixture neutralized with 3N sodium hydroxide. The organic phase was separated, and the aqueous phase was extracted with 250 ml of methylene chloride twice. The organic phases were combined, washed with water, dired over sodium sulfate, and concentrated in vacuo. The residue was crystallized from hexane to give 27.95 g of product, mp 71°-74°.
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