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.