Photodehydrocyclizations of stilbene-like compounds VIII: Synthesis of hexaheliceno[3,4-c]hexahelicene
The synthesis of a new double helicene, hexaheliceno[3,4-c]hexahelicene, has been described. Of two possible diastereomers only one has been obtained. Presumably the product has the racemic configuration but this assignment is not yet definite.
Conformational studies on hexahelicenes—I: The NMR spectra of the benzohexahelicenes
Abstract The NMR spectra of the benzohexahelicenes have been analyzed. The conformation of the helical structure is not changed to a large extent by the benzo-groups. Some flattening of a part of the helix results in a small downfield shift of the protons on the terminal rings and in a larger upfield shift of proton A in II ascribed to a change in the ring current in the pitch of the helix. A gradual upfield shift is found for protons of the terminal rings by an increase in overcrowding of the benzo-groups.
Chemie angeregter zustände—IV
Zusammenfassung Die Photocyclisierung der Distyrylbenzole erfolgt streng selektiv. Die aus den freien Valenzen und 1,6-Lokalisierungsenergien im 1. Anregungszustand erwarteten Cyclisierungsrichtungen stimmen mit den experimentellen Ergebnissen uberein.