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.
Photodehydrocyclizations in stilbene-like compounds—III
Abstract Photodehydrocyclizations in stilbene-like compounds take place only if the sum of the free valence numbers of the atoms concerned in the cyclization step exceeds in the excited state, a value of 1. If more than one cyclization is possible the photoconversion follows the pathway for which ΣF* is maximal; if ΔΣF* for various cyclizations is smaller than 0·1 a second product is sometimes formed. These rules also bold if only non planar and no planar products can arise. If planar as well as non planar compounds can be formed the main product is as a rule a planar polycyclic aromatic, even if ΣF* for its formation is lower than for other cyclizations. Sometimes but not always, a non planar product (with higher ΣF*) is found as a side product. The applicability of these rules in the planning of synthetic procedures for polycyclic aromatics is illustrated in the preparation of several new compounds (e.g. the four isomeric benzo hexahelicenes).
Die Pyrolyse Eines Gemisches von Benzol und Pyren
Die Pyrolyse eines Gemisches von Benzol und Pyren ergibt Biphenyl, 3-Phenyl-pyren (I), 1-Phenyl-pyren (II), 2.3-[o-Phenylen]-pyren (III), 2.3; 7.8-Di-[o-phenylen]-pyren (IV), 1.14; 10.11-Dibenzo-peropyren (V).und 1.14; 7.8-Dibenzo-peropyren (IV).