Ultrasound-Assisted Catalyst-Free Knoevenagel Condensation of Carbonyl Compounds with C – H Acids in Water

An ultrasound-assisted catalyst-free green protocol has been developed for the synthesis of a series of diversely substituted Knoevenagel condensation products from the reaction between functionalized aromatic aldehydes/isatin derivatives and substituted malononitriles as the C-H acids in water at ambient conditions. The method is simple, straightforward, and highly efficient. The major advantages of this newly developed protocol are expedient catalyst-free synthesis, good to excellent yields, energy efficiency, use of water as reaction medium, easy isolation of products, no need for column chromatographic purification, eco-friendliness, and operational simplicity.