Trapping of 1,8-Biradical Intermediates by Molecular Oxygen in Photocycloaddition of Naphthyl-<i>N</i>-(naphthylcarbonyl)carboxamides; Formation of Novel 1,8-Epidioxides and Evidence of Stepwise Aromatic Cycloaddition
and [4 + 4] cycloadducts, 3 and 4, respectively, novel 1,8-epidioxides (5) were formed under oxygen atmosphere. The transient absorption at lambda max of 360 nm with the lifetime of 360 ns was observed by laser flash photolysis of 1c and was interpreted as the absorption of biradical intermediate 2. On the basis of the anti stereochemistry of 5, which was different from that of the major [4 + 4] cycloadducts