Möbius‐Aromaticity and Antiaromaticity Driven Nucleophilic Substitution Reactions in Cycloheptatrienide Zwitterions with a Twisted Cycloheptatetraene Intermediate

Abstract

Pyridinium and phosphonium zwitterions featuring a cycloheptatrienide‐anion moiety are introduced into antiaromatic nucleophilic substitution reactions. The transformations afford other zwitterions, cycloheptatrienes or cycloheptatrienide salts. The initial reaction stage involves an elimination of pyridine or triphenylphosphine to form a Möbius‐aromatic cycloheptatetraene intermediate. The aromatic stabilization energy in parent cycloheptatetraene was estimated at 6–7 kcal/mol, an important value in terms of reaction rates. An anisotropy of the induced current density diagram illustrated the diatropic ring current confirming the aromaticity of the intermediate and an analysis of NICS values for the initial reaction step revealed a transition from a slightly antiaromatic to a moderately aromatic species. Therefore, these reactions are uniquely driven by both the relief of antiaromaticity and the acquisition of Möbius aromaticity.