Modulating Escape Channels of Cycloheptatrienyl Rhodium Carbenes to Form Semibullvalene

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