Fast, Solvent-Free, Microwave-Promoted Friedländer Annulation with a Reusable Solid Catalyst

A fast, solvent-free method is described for the synthesis of substituted quinoline derivatives via Friedländer cyclization, employing a reusable solid catalyst (silica-propylsulfonic acid). Although it worked best under microwave irradiation (with generally more than 90% isolated yields in 30 min), the reaction was also feasible under conventional heating (with fair to good yields in about 5 h).