Discovery of Deep-Seated Skeletal Rearrangements in the Photocyclizations of Some tert-Butyl-Substituted 1,2-Diarylethylenes.

The in-solution oxidative photocyclization of stilbenes to phenanthrenes is a well-known and synthetically valuable reaction. We report here our discovery that the oxidative photocyclization of several tert-butyl-substituted 1-styrylphenanthrenes resulted not only in the expected formation of tert-butyl-substituted picenes but also in the previously unknown rearrangement leading to the formation of tert-butyl-substituted pentahelicenes.