Ari Ayalon

Reductive ring closure of helicenes

Abstract Reduction of [5]-helicene ( 1 ) by alkali metal in THF yields a closed condensed polycyclic dianion i.e. benzo[ ghi ]perylene dianion ( 3 = ) The ring closure reaction takes place via a closed dihydro intermedate ( 2 = ).

Partitioning of charge in dibenzo[b,g]chrysene: the role of the system's topology

Dibenzo[b,g]chrysene dianion (32–) shows in its NMR spectrum a partitioning of charge. In the dianion most of the charge is located on the ‘anthracene’ moiety. These observations have been confirmed by MNDO calculations. In the calculations, the location of the lithium cation is taken into account. This unusual phenomenon is connected with the systems paratropicity and with its charge alternation. The NMR assignments were assisted by 2D techniques.

Reduction of pyracylene by alkali metals: Mechanism and formation of aggregates

Five reaction stages have been identified in the reduction of pyracylene to its dianion. The same stages were also observed in the photochemical oxidation starting with the dianion. The formation of dimers of anions and of mixed valence aggregates is discussed.