1,3,5 Trioxanetrione

The chemical compound 1,3,5-trioxanetrione, or 1,3,5-trioxacyclohexane-2,4,6-trione is a hypothetical oxide of carbon with formula C₃O₆. It can be considered a cyclic trimer of carbon dioxide (CO₂) or as a triple ketone of 1,3,5-trioxane (1,3,5-trioxacyclohexane).

Theoretical calculations indicate that the compound is unstable at room temperature (half-life less than 8 seconds); but may be stable at -196 °C.