Calcite and fluorite as catalyst for the Knِvenagel condensation of malononitrile and methyl cyanoacetate under solvent-free conditions

When milled together with calcite or fluorite, malononitrile and methyl cyanoacetate readily underwent Knövenagel condensation with aromatic aldehydes, giving the corresponding arylidenemalononitriles and (E)-α-cyanocinnamic esters in good to excellent yield.