Effective and Sustainable Access to Quinolines and Acridines: A Heterogeneous Imidazolium Salt Mediates C–C and C–N Bond Formation

Abstract

Quinoline and acridine derivatives have been prepared using a functionalized imidazolium salt as heterogeneous catalyst. Different ketones have been coupled with 2‐aminobenzaldehydes and 2‐aminoaryl ketones under solvent‐free conditions, employing 1,3‐bis(carboxymethyl)‐imidazolium chloride as a catalyst. The protocol is simple and effective for the synthesis of a variety of nitrogen containing heterocycles (> 35 examples) with moderate to excellent yields (up to 96 %), being possible to perform the reaction in preparative scale. Additionally, 3‐acetylquinolines have been transformed, under solvent‐free conditions, into quinolyl chalcone derivatives by means of the same catalyst. Thus, the catalytic system mediates both reactions effectively in a tandem procedure. Furthermore, the catalyst is easily separated from the reaction mixture and can be reused without loss of activity (up to 8 cycles) which remarks its sturdiness. The E‐factors are in the range of 14–23, both for the formation of quinolines and for the tandem reaction, which demonstrates the sustainability of the protocols described.