We describe the various escape channels available to
dirhodium
carbene intermediates from cycloheptatrienyl diazo compounds located
with density functional theory. An intramolecular cyclopropanation
would, in principle, provide a new route to semibullvalenes (SBVs).
A detailed exploration of the potential energy surface reveals that
methylating carbon-7 suppresses a competing β-hydride migration
pathway to heptafulvene products, giving SBV formation a reasonable
chance. During our explorations, we additionally discovered unusual
spirononatriene, spironorcaradiene, and metal-stabilized 9-barbaralyl
cation structures as local minima.