The Knoevenagel condensation of aromatic aldehydes with active methylene compounds such as malononitrile, ethyl cyanoacetate, benzimidazole-2-acetonitrile and benzothiazole-2-acetonitrile proceeded very smoothly, in a reusable and cheap choline chloride and urea based deep eutectic solvents. Both reaction time and yield are satisfactory. The advantages of this catalyst are that it is readily available
We demonstrated for the first time that [Nb10O28]6− exhibited base catalytic activity for aldol-type condensation reactions including Knoevenagel and Claisen–Schmidt condensation reactions.