Facile Formation Of A Möbius Molecule

The challenge of making a molecule that contains the distinctive twist of a Möbius strip and is also aromatic in character has long appealed to organic chemists. Now, researchers have made the first macrocycle to attain Möbius aromaticity without any assistance from metal coordination, temperature control, or protonation (J. Am. Chem. Soc., DOI: 10.1021/ja902836x). Eliminating those constraints allows chemists to conduct detailed investigations of Möbius aromaticity that would otherwise be impossible, the researchers note. The team, led by Dongho Kim of South Korea's Yonsei University and Atsuhiro Osuka of Japan's Kyoto University, managed to juggle both the twist and the necessary girth for aromaticity by expanding a porphyrin ring. They made their Möbius molecule—a benzopyrane-fused [28]hexaphyrin—by simply heating a 26-membered hexaphyrin in acetic acid at 130 °C for six hours. This reaction fuses a perfluorophenyl substituent into the porphyrin structure, creating the tricyclic benzopyrane system that imparts the strain necessary to achieve the twisted Möbius topology. Kim and Osuka hope to use the information they've gleaned from this structure to create a Möbius molecule that is antiaromatic.