A Möbius aromatic [28]Hexaphyrin bearing a diethylamine group: A rigid but smooth conjugation circuit

The reaction of [26]hexaphyrin with triethylamine in the presence of BF₃ OEt₂ and O₂ furnished a diastereomeric mixture of a diethylamine-bearing [28]hexaphyrin as a rare example of a Möbius aromatic metal-free expanded porphyrin. The Möbius aromaticity of these molecules is large, as indicated by their large diatropic ring currents, which are even preserved at 100 C, owing to their internally multiply bridged robust structure with a smooth conjugation network. These molecules were reduced with NaBH₄ to give an antiaromatic [28]hexaphyrin, and were oxidized with MnO₂ to give aromatic [26]hexaphyrins, both through a Möbius-to-Hückel topology switch induced by a C-N bond cleavage.