Photocycloaddition of cyanonaphthalenes to 1,3-cyclohexadiene

To prevent secondary processes due to facile thermal reaction, low-temperature irradiations of cyanonaphthalenes and 1,3-cyelohexadiene through a Pyrex filter were conducted. Along with the identification of the products, the results of the triplet-sensitized photoreaction of the irradiated mixture, low-temperature H-1 NMR study of the irradiated mixture, and the Cope rearrangement reaction of some products suggested that the primary major products are the corresponding exo-[4 + 4] adducts fused at 1,4 position of the naphthalene skeleton and the syn-[2 + 2] adducts fused at 1,2 position. The formations of the primary products in these singlet-state photocycloaddition reactions were interpreted by primary and secondary orbital interactions. A rationalization far the previous results on the photoreactions at room temperature was also provided.