Photochemistry of ω-(o-vinylphenyl)-ω′-(phenyl/2-furyl) butadienes: New approach to 4-substituted benzobicyclo[3.2.1]octadienes

Novel 1-(o-vinylphenyl)-4-(phenyl/2-furyl) butadienes (4a,b), synthesized in one step, undergo intramolecular photocycloaddition reaction to benzobicyclo[3.2.1]octadiene derivatives (6a,b) in very good yield (70–90%). In the case of phenyl derivative (4a) only endo-phenyl-benzobicyclo[3.2.1]octadiene isomer (endo-6a) was isolated whereas the furan (4b) derivative resulted in a mixture of endo- and exo-bicyclic isomer (6b). Phenyl benzobicyclo[3.2.1]octadiene derivative (endo-6a) underwent further di-π-methane rearrangement leading to tricyclic structure (endo-7a). The isolated compound 6a and the product of the rearrangement endo-7a were characterised by X-ray structure analysis.