When To Let GoDiradical Intermediates from Zwitterionic Transition State Structures?

Several
Brummond–Chen thermal intramolecular (2 + 2)-cycloaddition
reactions were examined using density functional theory calculations.
The results of these calculations indicate that it is possible for
these reactions to involve diradical intermediates that form directly
from zwitterionic transition state structures. The likelihood of this
scenario was shown to be sensitive to both the nature of substituents
and solvent polarity.