Process for preparing pradofloxacin
The invention relates to an improved process for preparing pradofloxacin, in which the substituent in the 7 position is introduced by nucleophilic substitution in an N-methylpyrrolidone-ethanol solvent mixture.
1. Process for preparing pradofloxacin of the formula (I)
by reacting, optionally in the presence of a base, the compound of the formula (II)
with (1S,6S)-2,8-diazabicyclo-[4.3.0]nonane of the formula (III)
in a solvent mixture of N-methylpyrrolidone and ethanol, wherein the solvent mixture contains 70 to 90% by weight of ethanol and 30 to 10% by weight N-methylpyrrolidone, wherein the reaction is performed at a temperature range of from 20 to 180° C.
2. Process according to claim 1 , wherein the (1S,6S)-2,8-diaza-bicyclo[4.3.0]nonane of the formula (III) is used in a molar ratio to the 7 chloro-8-cyano-1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acid of the formula (II) of 1:1.01 to 1:1.30.