To prevent secondary processes due to facile thermal reaction, low-tem
perature irradiations of cyanonaphthalenes and 1,3-cyelohexadiene thro
ugh a Pyrex filter were conducted. Along with the identification of th
e products, the results of the triplet-sensitized photoreaction of the
irradiated mixture, low-temperature H-1 NMR study of the irradiated m
ixture, and the Cope rearrangement reaction of some products suggested
that the primary major products are the corresponding exo-[4 + 4] add
ucts 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 prod
ucts in these singlet-state photocycloaddition reactions were interpre
ted by primary and secondary orbital interactions. A rationalization f
ar the previous results on the photoreactions at room temperature was
also provided.