The photosensitized oxygenation of semicyclic double bonds is highly sterically controlled. Little changes in the geometry of the ring system have a considerable influence on the direction of the reaction. This is demonstrated by the results of this reaction with methylencyclopentane, methylencyclohexane, methylencycloheptane, Δ1 (7)-p-menthene, Δ4 (8)-p-menthene, terpinolene and Δ2, 4 (8)-p-mentha-diene.
