2-oxoglutarate-dependent dioxygenase; part of the gene cluster that produces the tetronate natural products trihazones (PubMed:33570538). ThnC catalyzes the oxidative decarboxylation of trihazone A to trihazone D (PubMed:33570538). The C4 hydrogen is first abstracted by the iron-oxo species generated in ThnC to give a tertiary radical at C4 (PubMed:33570538). This is followed by decarboxylation and removal of the second electron by the FeIII-OH center to give trihazone D (PubMed:33570538). The pathway begins with the formation of trihazone A by the hybrid PKS-NRPS synthetase thnA and the trans-enoyl reductase thnE. Trihazone A is further decarboxylated by the 2-oxoglutarate-dependent dioxygenase thnC to produce trihazone D. The function of the FAD-dependent monooxygenase thnD has still to be identified (PubMed:33570538). Binds 1 Fe(2+) ion per subunit. Secondary metabolite biosynthesis. Belongs to the iron/ascorbate-dependent oxidoreductase family.