Thermal valence isomerization of cis-fused bicyclic cyclobutenes. A study of orbital symmetry control

Article abstract of DOI:10.1021/ja00399a025

This study shows that thermally promoted valence isomerizations of cis-fused bicyclic cyclobutenes, when free of steric constraint, yield products arising from both orbital symmetry allowed conrotatory openings of the labile σ bond in the cyclobutene ring. In the case of the related vinylcyclobutenes, one conrotatory mode produces a stable cis,trans,cis monocyclic triene whereas fission in the other allowed sense affords a thermally labile trans,cis,cis monocyclic triene which, in turn, cyclizes to yield a cyclohexadiene derivative. The product distributions are evaluated in terms of secondary orbital interactions.