Pechmann Reaction in Chloroaluminate Ionic Liquid

Abstract

Substituted coumarins were synthesized in good yields via the Pechmann reaction in chloroaluminate ionic liquid. 1-Butylpyridinium chloroaluminate ionic liquid was used as a solvent cum catalyst for this condensation reaction.

Synthesis and Nitration of 7-Hydroxy-4-Methyl Coumarin via Pechmann Condensation Using Eco-Friendly Medias

“…The reactions were clean and affording exclusively coumarins in high yields in a relatively short time. It is an established fact in the literature that pechmann reaction proceeds through transesterification and intramolrcular hydroxyalkylation, followed by dehydration [18,24]. These three steps are all typical acid catalyzed reactions.…”

“…Recently, Knoevanagel condensation is reported to proceed with high selectivity and reactivity in the formation of coumarins over solid base catalysts [16]. Microwave irradiation accelerates these reactions several-fold with better yields of the products where the reactants, however, are taken in millimoles quantities [17,18]. Some important coumarins have been synthesized in 1-butyl pyridinium chloroaluminate ionic liquid in good yields [19] and also in indium (III) chloride [20].…”

Recent advances in ionic liquids: green unconventional solvents of this century: part II

“…1-Butyl-3-methylimidazolium chloroaluminate, [bmim]Cl ×2AlCl 3 IL was the first IL (Scheme 11) which was used as an alternative to conventional acid catalysts in the Pechmann condensation of phenols with ethyl acetoacetate leading to the formation of coumarin derivatives by Potdar (95). Similar chloroaluminate IL was used by Khandekar and Khadilkar for the synthesis of substituted coumarins to obtain coumarins in good yields, and they employed 1-Butylpyridinium chloroaluminate IL as a solvent cum catalyst for this condensation (96). But these chloroaluminated ILs are very sensitive to hydrolysis; traces of water can change the composition of the melt and the concentration of protons.…”

Synthetic Uses of Phenols

“…The methodology works well when the dehydration reaction can be controlled as in the classical Pechmann reaction, which is the condensation of β-ketoesters and phenols to give coumarins 149 . The reaction is accelerated by applying microwave irradiation or using an ionic liquid as the solvent 150,151 . A zeolite catalyst allows the synthesis of coumarins from acetic anhydride and phenols with concomitant Claisen condensation 152 .…”