Water → (RS)-3-ethoxycarbonyl-7,9-difluoro-1-methyl-8-(3-methyl-1-piperazinyl)-4-oxo-1,4-dihydro-benzo[b][1,8]naphthyridine

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Reaction Steps

A suspension of 2 g of 3-ethoxycarbonyl-7,8,9-trifluoro-1-methyl-4-oxo-1,4-dihydrobenzo[b][1,8]naphthyridine in 30 cm3 of dimethyl sulphoxide and 5 g of 2-methylpiperazine is heated at a temperature close to 100° C., with stirring, for 2 hours. The solution obtained is poured, at this temperature, with stirring, into a mixture of 150 cm3 of water and 50 g of ice. 5 g of potassium carbonate are added at about 20° C. and the mixture is extracted with 3 times 50 cm3 of trichloromethane. The combined organic extracts are washed with twice 50 cm3 of water, dried over magnesium sulphate, filtered and concentrated to dryness under reduced pressure (20 kPa) at about 50° C. The residue obtained is recrystallized from 30 cm3 of ethanol. 1.6 g of (RS)-3-ethoxycarbonyl-7,9-difluoro-1-methyl-8-(3-methyl-1-piperazinyl)-4-oxo-1,4-dihydrobenzo[b][1,8]naphthyridine are obtained in the form of a yellow solid melting at 240° C.

Provenance & Evidence