Crystal structure and identification of resonance forms of diethyl 2-(3-oxoiso-1,3-di­hydro­benzo­furan-1-yl­idene)malonate

The reaction of diethyl malonate with phthaloyl chloride in aceto­nitrile in the presence of tri­ethyl­amine and magnesium chloride results in the formation of the title compound, diethyl 2-(3-oxo-1,3-di­hydro-2-benzo­furan-1-yl­idene)propane­dioate, C(15)H(14)O(6). One of the ester groups of the diethyl malonate fragment is almost coplanar with the isobenzo­furan unit, while the plane of the other group is perpendicular to it [dihedral angles = 5.45 (3) and 83.30 (3)°, respectively]. The C—C and C—O distances both in the heterocyclic furan ring and the diethyl malonate fragment are indicative of the dipolar delocalization occurring within the isobenzo­furan unit. This delocalization is likely to be responsible for the unusual inter­molecular O⋯O contact [2.756 (2) Å], established between the O atom of the furan ring and the carbonyl O atom of the diethyl malonate fragment. In the crystal, weak C—H⋯O inter­actions are observed, which link the mol­ecules into [100] chains.