Stilbene photocyclization

Stilbene photocyclization is the coupling of two aromatic carbons in stilbenes upon ultraviolet irradiation. The reaction can be used to form polycyclic aromatic hydrocarbons and heteroaromatics. Stilbene photocyclization is the coupling of two aromatic carbons in stilbenes upon ultraviolet irradiation. The reaction can be used to form polycyclic aromatic hydrocarbons and heteroaromatics. Under UV irradiation, stilbene and its derivatives undergo intramolecular cyclization to form dihydrophenanthrenes. In the presence of an oxidant, the dihydrophenanthrene aromatize to give polycyclic aromatics result. Typically, the dihydrophenanthrenes themselves are relatively unstable, and revert to cis-stilbenes in the absence of a hydrogen-trapping agent. Suitably substituted stilbenes may undergo irreversible, rearomatizing elimination or -shift processes in the absence of an oxidant. Aryl enynes, heteroatomic stilbene derivatives (e.g. amides), and substrates containing a single heteroatom in place of the stilbene double bond also undergo the reaction.