Advantageous Use of Ionic Liquids for the Synthesis of Pharmaceutically Relevant Quinolones

The advantageous use of ionic liquids (ILs) as alternatives to common DMF as solvent in the Grohe cycloaracylation for the synthesis of pharmaceutically relevant quinolones is reported. ILs showed in many cases shorter reaction times and higher yields, complete conversions of the reactants and easy work-up procedures compared with DMF. Of the ILs screened, tributylmethylammonium methanesulfonate ([TBMA][MsO]) was selected as the most suitable for further studies. Interestingly, a wide substrate scope was observed and the IL was recycled by a green process. A further step forward in the use of [TBMA][MsO] for quinolone synthesis was the preparation by a one-pot/three-step procedure of the representative 3-carboxy-4-quinolone acid 16, which was obtained in high yield in a short time. The greener properties of ILs in comparison with DMF and their non-volatility appoint this method as a potentially efficient and alternative approach to the industrial production of quinolones.