Knoevenagel Reaction Catalyzed by a Reusable Bronsted Acid Based on 1-Alkyl-1,2,4-triazolium Tetrafluoroborate

The Knoevenagel reaction is one of the most useful methods for the synthesis of α,β- unsaturated nitriles. We disclose an efficient protocol for the Knoevenagel reaction of aldehydes with malononitrile catalyzed by 1-alkyl-1,2,4-triazolium salts to afford the corresponding products in excellent yields. The important feature of this reaction is the catalyst; 1-alkyl-1,2,4-triazolium salts are recycled and reused. Furthermore, the reaction conditions are environment friendly and do not produce any hazardous waste.