113028-17-4

Ethyl 6-fluoro-1-methyl-4-oxo-7-(1-piprazinyl)-4H-[1,3]thiazeto[3,2-a]quinoline-3-carboxylate is an off-white to slightly yellow powder used as an intermediate for prulifloxacin.

The general procedure for the synthesis of ethyl 6-fluoro-7-piperazine-1-methyl-4-oxo-1,4-dihydro-[1,3]thiazepine[3,2-a]quinoline-3-carboxylate from ethyl 6,7-difluoro-1-methyl-4-oxo-1,4-dihydro-[1,3]thiazepine[3,2-a]quinoline-3-carboxylate and piperazine was carried out as follows: 50 g of ethyl 6,7-difluoro-1-methyl-4 -oxo-4H-[1,3]thiazino[3,2-a]quinoline-3-carboxylic acid ethyl ester was dissolved in 5 volumes of DMSO and heated to 60 °C. Subsequently, 40 g of piperazine was added and the reaction was kept stirred at 60°C for 4 hours. After completion of the reaction, the mixture was cooled to room temperature, 5 volumes of acetonitrile was added and stirring was continued at room temperature for 4 hours. The precipitate was collected by filtration and dried to give 52.8 g of ethyl 6-fluoro-7-piperazine-1-methyl-4-oxo-[1,3]thiazolocyclo[3,2-a]quinoline-3-carboxylate in 87% yield. After further purification, the yield of ethyl 6-fluoro-7-piperazine-1-methyl-4-oxo-[1,3]thiazolocyclo[3,2-a]quinoline-3-carboxylate was up to 99%.

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[5] Patent: WO2009/93268, 2009, A1. Location in patent: Page/Page column 15