The Role of Strain in the Homoaromatization of Semibullvalenes.

The low activation barrier to the Cope rearrangement of semibullvalenes has been attributed to the inherent ring-strain of this nucleus. Appropriate, Dewar-Hoffmann, substitution of semibullvalene results in the stabilization of the transition state and a further lowering of the Cope barrier. An alternative proposal for lowering/eliminating this barrier is the use of strain to destabilize the localized semibullvalene. Using density functional and Hartree-Fock calculations, we predict that additionally straining the semibullvalene nucleus, by small ring annelations, will lead to a lowering of the Cope barrier and ultimately to ground state neutral homoaromatics. [ABSTRACT FROM AUTHOR]