Vinylcyclopropyl Anion: Structure, Reactivity, Thermodynamic Properties, and an Unusual Rearrangement

Vinylcyclopropane (1) is deprotonated in the gas phase by NH₂ ^- or Me₂N^- to afford its conjugate base (1a). Vinylcyclopropyl anion is quite basic (ΔH_acid(1) = 394 ±3 kcal mol^-1), has a relatively small electron binding energy (12 ± 5 kcal mol^-1), and reacts with a variety of reagents including N₂O, CS₂, COS, O₂, and SO₂. The reaction of 1 with OH^- (ΔH_acid(H₂O) = 390.7 kcal mol^-1) leads to a surprising rearrangement and the formation of the conjugate base of methylenecyclobutane (2a). A mechanism is proposed to account for this unusual reaction and it is in accord with ab initio molecular orbital calculations. In particular, the orbital symmetry allowed (σ_2s + π_4s) transition state leading to 2a is slightly preferred over the conrotatory ring opening of 1a (1.2 kcal mol^-1 (MP2/6-31+G*//6-31+G*)).