Sequential Transition States and the Valley−Ridge Inflection Point in the Formation of a Semibullvalene

Two sequential transition states are calculated at the B3LYP/6-31G(d,p) level for the deazetization of 3b. The intrinsic reaction coordinate for loss of nitrogen passes through a transition state and then a valley−ridge inflection point and ultimately leads to the transition state for the Cope rearrangement of semibullvalene 4b. The energetic and geometrical consequences are discussed.