Aromaticity of the Bergman, Myers-Saito, Schmittel, and directly related cyclizations of enediynes.
Aromaticity criteria (magnetic susceptibility exaltations, nucleus independent chemical shifts (NICS), and aromatic stabilization energy (ASE) evaluations) for enediyne and enyne-allene cyclizations evaluated at (UBS)-BLYP/6-31G* all agree that the degrees of cyclic electron delocalization of the benzenoid systems formed by the Bergman (3) and Myers-Saito reactions (5) are comparable to benzene. The reaction enthalpy differences between the parent cyclizations and their benzannelated analogues are not entirely due to disparities in gained ASE during the reactions. The alternative formation of fulvene biradicals is not accompanied by favorable aromatic effects.
Stahl
Frank
F
Institut für Organische Chemie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Henkestr. 42, 91054 Erlangen, Germany.
Moran
Damian
D
von Ragué Schleyer
Paul
P
Prall
Matthias
M
Schreiner
Peter R
PR