Photoinduced Skeletal Rearrangement of Diarylethenes: Photorelease of Lewis Acid and Synthetic Applications

The
skeletal photorearrangement including 6π-electrocyclization
induced by UV light of ortho-halogen-substituted
diarylethenes has been studied. It has been found that the reaction
pathways leading to bi- or tricyclic frameworks depend on the kind
of halogen substituent and solvent. Photocyclization with halogen
abstraction leads to bicyclic fused aromatics, while the tricyclic
frameworks are formed due to the tandem 6π-electrocyclization/sigmatropic
shift reaction. THF is preferred as the solvent in the former process
and chloroform in the latter reaction. It was found for the first
time that, owing to the ability of this series of diarylethenes to
undergo skeletal photorearrangement with the release of the bromide
cation, they can be used both as brominating agents and as Lewis acids
for catalyzing electrophilic reactions.