Hexamethylphosphoramide → 1-Cyclopropyl-7-(2,6-dimethylpyridinyl)-5,6,8-trifluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acid

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Reaction Steps

A mixture of 2.8 g ethyl 7-bromo-1-cyclopropyl-5,6,8-trifluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylate, 2.2 g 2,6-dimethyl-4-(trimethylstannyl)pyridine (Example 1, part g), 2 ml hexamethylphosphoramide, 320 mg dichlorobis(triphenylphosphine)palladium and 50 ml dioxane was stirred and heated under reflux in an argon atmosphere for 24 hours. The reaction mixture was concentrated to dryness and the residue was treated with 100 ml of 1N hydrochloric acid and heated at reflux for 2 hours. The latter mixture was filtered and the filtrate concentrated to dryness. The residue was dissolved in 50 ml 5% aqueous potassium carbonate, decolorized with charcoal and filtered. The filtrate was acidified with concentrated hydrochloric acid, sodium acetate added, and the resulting precipitate was collected, dried and recrystallized from ethanol to give 1.6 g 1-cyclopropyl-7-(2,6-dimethylpyridinyl)-5,6,8-trifluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acid as a cream-colored solid, m.p. 264°-266° C.

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