Non-heme dioxygenase catalyzing the conversion of thebaine to neopinone. Catalyzes also, with lower efficiency, the 6-O-demethylation of oripavine to morphinone. No activity with (S)-reticuline, salutaridine, papaverine, (S)-corytuberine, (S)-scoulerine, pavine, noscapine or codeine. 2-oxoglutarate + O2 + thebaine = CO2 + formaldehyde + neopinone + succinate Binds 1 Fe(2+) ion per subunit. Moderate substrate inhibition. Not inhibited in vitro by acylcyclohexanediones. Alkaloid biosynthesis; morphine biosynthesis. Neopinone spontaneously rearranges to the more stable codeinone. Belongs to the iron/ascorbate-dependent oxidoreductase family.