Photoisomerization of Highly Alkylated Butadienes

Abstract

Bicyclobutane formation and a 1,5 H shift, and not photocyclization to the cyclobutene derivative, predominate on the irradiation of highly alkylated nonplanar 1,3-dienes 1. Bicyclobutanes 2 are also formed from dienes with two central tBu groups, whereas the corresponding iPr-substituted compounds afford almost exclusively 3. For dienes with an iPr and a tBu group, the two pathways are almost equally likely to occur.