Study on the Pd/C‐Catalyzed (Retro‐)Michael Addition Reaction of Activated Methylene Compounds to Electron‐Poor Styrenes
Palladium on carbon (10% Pd/C) efficiently catalyzes the (retro-)Michael addition of activated methylene compounds 2a-d, such as malononitrile (2b), to mono- and doubly activated styrenes 1a-h to give the adducts 3a-1. The scope and limitations are described. The Knoevenagel condensation reaction of benzaldehyde and 2b or ethyl cyanoacetate (2c) is also catalyzed by 10 % Pd/C. In these cases the Michael adducts can even be prepared in a three-component reaction. A mechanism, with as first step the oxidative addition of 2a-d to Pd 0 , is proposed.