The enzyme is involved in the biosynthesis of the phytotoxin solanapyrone in some fungi. The bifunctional enzyme catalyses the oxidation of prosolanapyrone II and the subsequent Diels Alder cycloisomerization of the product prosolanapyrone III to (-)-solanapyrone A (cf. EC?1.1.3.42, prosolanapyrone II oxidase).