Thermodynamically Stable o-Quinodimethane: Synthesis, Structure, and Reactivity.

T hermal isomerization of cyclobutaphenanthrene to  o - quinodimethane was investigated. Sterically congested substituents or electron-donating substituents on the four-membered ring promoted the ring-opening, affording  o - quinodimethane in a relatively stable form. Isolation of the newly prepared  o - quinodimethane allowed its structural elucidation and investigation of its potential reactivities. Dual [4+2] cycloaddition of an aryne and  o - quinodimethane afforded tetrabenzopentacene, demonstrating the synthetic application of the isolated compound.