Triethylammonium Hydrogen Sulfate [Et3NH][HSO4] as an Efficient Ionic Liquid Catalyst for the Synthesis of Coumarin Derivatives

Triethylammonium hydrogen sulfate [Et3NH][HSO4] has been studied to be an efficient ionic liquid catalyst for the synthesis of biologically potent coumarin derivatives. Thus, 4-substituted coumarins have been synthesized through the Pechmann condensation of phenols with beta-ketoesters in the presence of [Et3NH][HSO4]. Also, 4-hydroxycoumarin was reacted with various aldehydes using this catalyst to obtain the alpha,alpha '-benzylidene bis(4-hydroxycoumarin) derivatives. In addition, this efficient and privileged ionic liquid catalyst has been described in the synthesis of pyrano[3,2-c]coumarin derivatives by condensation of 4-hydroxycoumarin with chalcones. The optimization conditions carried out in the present study revealed that 20 mol% of ionic liquid catalyst under solvent-free condition at 110 degrees C are the best conditions for the synthesis of coumarin-derivatives in good to excellent yields. The present methodology is a facile and green approach offering several advantages, such as excellent yield of products, minimizing production of chemical wastes, shorter reaction profile, mild reaction conditions, simple operational procedure, and easy preparation/separation of catalyst as a non-corrosive and stable ionic liquid.