3-[1-(Ethylamino)ethylidene]-6-methyl-3H-pyran-2,4-dione.

The structural results clearly indicate that 3-[1-(ethylamino)ethylidene]-6-methyl-3H-pyran-2,4-dione exists as a keto-enamine tautomer in the solid state. The H atom bonded to N(9) refines with a normal temperature factor and the bond distance of the keto group [C(4)--O(13)] of 1.263 (1) A is elongated due to resonance. This resonance is also indicated by an averaging of the single bonds [C(2)--C(3), C(3)--C(4), C(4)--C(5) and C(8)--N(9)] and double bonds [C(3)--C(8) and C(4)--O(13)] in the crystal structure and by the fact that not only is the pyran ring planar [r.m.s. deviation 0.0212 (9) A] but also there is planarity for the whole molecule [r.m.s. deviation 0.074 (1) A]. A strong intramolecular hydrogen bond is found between the 4-oxo group and the amine H atom.