c5h4o2

from The Collaborative International Dictionary of English v.0.48

Pyrone \Py`rone\, n. [G. pyron, an abbr. of pyrokoman.] (Org.
   Chem.)
   An unsaturated cyclic compound, {C5H4O2}, of which two
   varieties are known, [alpha] and [gamma]. [gamma]-pyrone is
   the parent substance of several natural yellow dyestuffs.