Phosphoric Acid → 9-fluoro-8-chloro-5-methyl-6,7-dihydro-1-oxo-1H,5H-benzo[ij]quinolizine-2-carboxylic acid

Participants

Reaction Conditions

Reaction Steps

A mixture of 1.5 g of 6-fluoro-5-chloro-1,2,3,4-tetrahydroquinaldine and 1.8 g of diethyl ethoxymethylenemalonate was heated at 160° C. for 30 minutes. Then, 14 g of polyphosphoric acid prepared from 7 g of phosphorus pentoxide and 7 g of phosphoric acid was added to the mixture and the resulting mixture was allowed to react by heating at 140° to 150° C. for 1 hour. After completion of the reaction, the reaction mixture was poured onto 100 g of ice, followed by adjusting the mixture to pH 6 to 7 with a 10 N aqueous sodium hydroxide solution. The precipitates were collected by filtration and added to 30 ml of concentrated hydrochloric acid followed by heating under reflux. After completion of the reaction 50 ml of water was added to the reaction mixture to precipitate crystals. The crystals thus-obtained were collected by filtration, washed with water and dried. Recrystallization of the crude crystals from ethanol gave 1.2 g of 9-fluoro-8-chloro-5-methyl-6,7-dihydro-1-oxo-1H,5H-benzo[ij]quinolizine-2-carboxylic acid as white rhombic crystals having a melting point of 297° to 298° C.

Provenance & Evidence