Synthesis and structure of 2,4-bis(2,6-dimethyl-4 <i>H</i> -pyran-4-ylidene)-3-oxopentanedinitrile, an unexpected product of a Knoevenagel condensation reaction

The title com-pound, C₁₉H₁₆N₂O₃, was the unexpected product of the Knoevenagel condensation between 2,6-dimethyl-γ-pyrone and cyano-acetic acid in the presence of acetic anhydride and piperidine as catalyst. The mol-ecule is formed by two almost planar 2,6-dimethyl-4<i>H</i>-pyran-4-cyanoyl-idene halves connected by the central carbonyl group. The two halves are not coplanar, the dihedral angle between their planes being 47.51 (3)°. The packing shows the formation of (001) sheets of mol-ecules held together by weak C-H⋯N and C-H⋯O hy-dro-gen bonds. A mechanism for the reaction is proposed.