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Microwave-assisted synthesis of new substituted anilides of quinaldic acid
Published: 31 October 2011 by MDPI in The 15th International Electronic Conference on Synthetic Organic Chemistry session Microwave Assisted Synthesis
Abstract: Derivatives of quinoline and its isosters are remarkable compounds with many different kinds of biological effects. A number of quinoline related compounds expressed antifungal, antibacterial, antiviral, antineoplastic, and other activities. In order to perform the classical synthesis of amides activation of quinoline-2-carboxylic acid is usually required. When activation is carried out under standard conditions with thionyl chloride, formation of undesired chloro compound where chlorine is attached in position 4 of quinoline ring is observed. In this study we have developed a method for preparation of substituted anilides in one step, based on the direct reaction of an acid or ester with substituted anilines using microwave irradiation. In recent developments, the use of microwave irradiation to simplify and improve classic organic reactions has become a very popular method, because it often leads to higher yields, cleaner reactions and shorter reaction times. In connections with solvent-free conditions, microwave-assisted methods result in very efficient and environmentally friendly technology. The method was tested on compounds: 2-quinaldic acid and its methyl and phenyl ester, 2-naphthoic acid and its ethyl ester. All those compounds reacted with 4-bromaniline as a model aniline. The synthesis was carried out under solvent-free conditions or in solvents: DMF and chlorobenzene. Despite the fact, that formation of anilides under microwave irradiation is hampered by competitive decarboxylation of quinaldic acid to quinoline, this technique showed certain advantages like shorter reaction time, no use of aggressive chemicals and simpler work-up. From the series of experiments is evident, that the use of phenyl ester is the most effective for microwave accelerated synthesis of anilides. A series of substituted anilides of quinaldic acid were prepared by developed method.
Keywords: microwave, amide formation, quinaldic acid