A Preferred Disrotatory 4n Electron Möbius Aromatic Transition State for a Thermal Electrocyclic Reaction

Abstract

Not forbidden: Thermal 4n electron electrocyclic reactions of Hückel topology structures proceed via "allowed" conrotatory pathways. However, for a Möbius topology, the Woodward-Hoffmann rules may be reversed and a "forbidden" disrotatory pathway can be preferred as shown theoretically for dodecahexaene 1 that transforms via a Heilbronner-Möbius aromatic transition structure 2 into a cyclic polyene 3.