Tetronic acid is a chemical compound, classified as a ó-lactone, with the molecular formula C<sub>4</sub>H<sub>4</sub>O<sub>3</sub>.
It interconverts between keto and enol tautomers:
Many natural products such as ascorbic acid (vitamin C), penicillic acid, pulvinic acids, and abyssomicins possess the ò-keto-ó-butyrolactone motif of tetronic acid.
In organic synthesis, it is used as a precursor for other substituted and ring-fused furans and butenolides. It is also forms the structural core of a class of pesticides, known as tetronic acid insecticides, which includes spirodiclofen and spiromesifen.