The Knoevenagel condensation between an active methylene compound and an aromatic aldehyde with a carbamic acid ammonium salt used as an organocatalyst gave the desired Knoevenagel products in up to 98% yield. The reaction occurred at rt and in a short reaction time under solvent-free conditions. In addition, no extraction, wash, or chromatography steps were needed to obtain a high-purity Knoevenagel product.
![ethyl 2-[(4-chlorophenyl)methylidene]-3-oxobutanoate结构式](https://image.chemsrc.com/caspic/388/19411-80-4.png)
![dimethyl 2-[(4-chlorophenyl)methylidene]propanedioate结构式](https://image.chemsrc.com/caspic/070/52927-44-3.png)