Background: Quinolines are one of the most popular N-heteroaromatic compounds incorporated
into the structures of many pharmaceuticals. The classical methods for the synthesis of quinoline
derivatives include Skraup, Doebner–Von Miller, Conrad–Limbach, Combes, and Pfitzinger quinoline
syntheses but the best-known method for the preparation of quinolines is Friedlander quinoline
synthesis. A number of methods have been reported for the synthesis of quinolines involving a variety
of catalysts. However, many of these procedures are not satisfactory because of harsh reaction conditions,
poor yields, prolonged time period, and use of hazardous and often expensive catalyst. Hence,
mild synthetic protocol for the synthesis of quinolines is highly desirable.
Objective: Mild and efficient synthesis of quinolines in the presence of sulfonyl functionalized imidazolium
ionic liquids is presented in this manuscript.
Method: Various functional quinolines were synthesized by one–pot condensation reaction of 2–
aminoaryl carbonyl compounds with an activated α–CH acid such as cyclic or acyclic β–dicarbonyl or
aromatic carbonyl compounds in the presence of recyclable sulfonyl functionalized imidazolium ionic
Results: Sulfonyl functionalized imidazolium ionic liquids exhibited remarkable activity towards synthesizing
a broad range of quinolines and 1-(4-sulfonylbutyl)-3-methylimidazolium trifluoromethanesulfonate
ionic liquid was found to be most efficient compared to other ionic liquids used for the
synthesis of parallel library of quinolines.
Conclusion: A cascade protocol for the synthesis of functional quinolines is developed by the condensation
of 2-amino-5-chlorobenzophenone (or 2-aminobenzophenone) with a variety of cyclic or
acyclic β-diketones or aromatic ketones in the presence of SO3H-functionalized ILs. The recyclability
of ionic liquids, simple work-up procedure, short reaction time and high yields are the important attributes
of the present protocol.