The Photosensitized Oxygenation of Furanoeremophilanes. I. The Isomeric Hydroperoxides from Petasalbin and Their Transformations to Lactones

The photosensitized oxygenation of petasalbin I gave almost quantitatively a crystalline mixture of two isomeric hydroperoxides, V-a and V-b, both of which were then transformed to the corresponding lactones, VI-a and VI-b, respectively, in good yields. The stereochemistry of these hydroperoxides and lactones has been established by spectral and chemical methods. Furthermore, two natural lactones, III and IV, were prepared by the reduction of the hydroperoxides.