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

The title compound, C19H16N2O3, was the unexpected product of the Knoevenagel condensation between 2,6-dimethyl-γ-pyrone and cyanoacetic acid in the presence of acetic anhydride and piperidine as catalyst. The molecule is formed by two almost planar 2,6-dimethyl-4H-pyran-4-cyanoylidene 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 molecules held together by weak C - H⋯N and C - H⋯O hydrogen bonds. A mechanism for the reaction is proposed.