The selectivities of the oxidations of β-ionone 1 were switched by the organoselenium catalyst used. [3,5-(CF3)2C6H3Se]2 led to (E)-5,6-epoxy-β-ionone (2, 72% yield), while (PhCH2Se)2 gave the major Baeyer–Villiger oxidation product 3 in excellent yield (91%).