(617fj) Base-Free Knoevenagel Condensation Catalyzed By Different Heterogeneous Copper Catalysts

The famous Knoevenagel condensation is a widely used reaction in research and industry and has been of importance for several pharmaceutical products. Generally this reaction is catalyzed by organo-bases, such as pyridine or piperidine, but using these homogeneous base catalysts often leads to time consuming work-up procedures. Heterogeneous catalysts would solve such a problem. Therefore, we explored different nanomaterials which might catalyze this reaction. This lead to the discovery of copper as a reative species.

For the first time the Knoevenagel condensation was catalyzed by different forms of elemental copper with high activity and excellent isolated yields. Different sizes & surface functionalities of copper nanoparticles showed different conversion rates. Carbon-coated copper nanoparticles showed low conversion whereas naked, comercially available copper nanoparticles exhibited high activity. It was assumed that the reduced copper surface is the active catalytic site. A succesful scale up (>100 g) reaction was performed without any separation or chormatography resulting in 91 % isolated yield .

Schneider, E.M; Zeltner M.; Kraenzlin N.; Grass R. N.; Stark W. J. Chem. Commun., 2015,51, 10695-10698