Cyclization of Stilbene and its Derivatives

It was, however, soon recognized that this type of process was common for many 1,2-diarylethenes and that the mechanism proceeded by photoinduced 6

π

-electrocyclization of the

cis

-isomer to give the

trans

4a,4b-dihydrophenanthrene, which was readily oxidized by air or iodine to the arene (Figure 33.1).