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

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.