Synthesis of norfloxacin analogues catalyzed by Lewis and Brönsted acids: An alternative pathway

An alternative synthetic pathway to prepare norfloxacin analogues is presented. Three Lewis acids (CeCl3·7H2O, AlCl3·6H2O, ZnCl2) and one Brönsted acid (TsOH) were tested as catalysts in the preparation of 3,4-difluoroacrylate. Cyclization of this acrylate at 55 °C was achieved with the use of Eaton's reagent (P2O5/MeSO3H) a known Brönsted acid. The fluoroquinolone-boron complex presented high yields on C-7 nucleophilic substitution of the fluorine atom by different heterocyclic amines with low, medium and strong nucleophilic character.