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.

Automated summary

An interest in developing new 2-acetyl/propanoyl quinolines via Friedlander synthesis has been extensively studied. In this work, we successfully synthesized 2-acetylquinolines in high yields by using a freshly prepared Eaton's reagent as a catalyst without solvents. We also reported a novel regioselective solvent-free reaction for the synthesis of o-aminoarylketones with unsymmetrical 1,2-diketone, yielding different 2-propanoylquinolines. Eaton's reagent played a unique role in the reaction as a powerful desiccant, condensing agent, cyclizing agent, and dehydrating agent. It was found that Eaton's reagent is an inexpensive and easily accessible catalyst for the Friedlander synthesis.