3-Methyl­ideneoxolane-2,5-dione

The title compound (itaconic anhydride), C₅H₄O₃, consists of a five-membered carbon–oxygen ring in a flat envelope conformation (the unsubstituted C atom being the flap) with three exocyclic double bonds to two O atoms and one C atom. In contrast to the bond lengths, which are very similar to those in itaconic acid in its pure form or in adducts with other mol­ecules, the bond angles differ significantly because of the effect of ring closure giving rise to strong distortions at the C atoms involved in the exocyclic double bonds. In the crystal, C—H...O inter­actions link the mol­ecules, forming an extended three-dimensional network.