Solvent-Free Synthesis of New Quinoline Derivatives via Eaton's Reagent Catalysed Friedlander Synthesis

An interest for the development of new 2-acetyl/propanoyl quinolines via Friedlander synthesis is one of the most studied synthetic approaches. Herein we report the use of a freshly prepared Eaton's reagent (phosphorus pentoxide in methanesulfonic acid) as catalyst without solvents to obtain quinoline derivatives. Eleven 2-acetylquinolines were synthesized in high yields (85-96%) from symmetrical 1,2-diketone, butan-2,3-dione with o-aminoarylketones in the presence of Eaton's reagent. Subsequently, a novel regioselective solvent free reaction is reported for synthesis of o-aminoarylketones with unsymmetrical 1,2-diketone, pentan-2,3-dione, to yield different 2-propanoylquinolines. Eaton's reagent performs a unique way of this reaction as a powerful desiccant, condensing, cyclizing and dehydrating agent. Among these advantages of Eaton's reagent was found as an inexpensive and easily accessible catalyst for the Friedlander synthesis.