The tetraphenylporphyrin-sensitized photooxygenation of 1, 3, 5-cycloheptatriene at subambient conditions affords the norcaradiene (2+4)-cycioadduct 2b (3.5%), the tropilidene (2+4)-2a (40%) and (2+6)-cycloadducts 2c (37%), benzaldehyde (5%), and benzene (5%). The characterization of these novel endoperoxides was made on the basis of 1H and 13C NMR spectral data, elemental analyses, diimide reduction to the corresponding saturated cyclic peroxides, and catalytic reduction. © 1979, American Chemical Society. All rights reserved.