Benzocyclobutenone enolate: An anion with an antiaromatic resonance structure

Benzocyclobutenone enolate (1a) was synthesized by deprotonating its conjugate acid with fluoride ion in the gas phase using a Fourier transform mass spectrometer. Reactions of 1a were explored and C-alkylation was found to be greatly preferred over oxygen attack. Thermodynamic properties (ΔH○_acid(1) = 360.3 ± 2.1 kcal mol^-1, EA(benzocyclobutenyl radical) = 1.90 ± 0.10 eV, and BDE(C-H) = 90.5 ± 3.1 kcal mol^-1) also were measured. The results are contrasted to ab initio calculations on cyclobutanone, benzocyclobutenone, and cyclobutenone enolates. Natural bond orbital and Bader analyses are reported too. Given our gas phase and computational results, we were able to devise conditions for the generation and trapping of 1a in tetrahydrofuran despite previous failings reported in the literature.