Synthesis and structure of 2,4-bis-(2,6-dimethyl-4H-pyran-4-yl-idene)-3-oxo-penta-nedi-nitrile, 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-4H-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.