Helicenes: Synthèse Photochimique Et Étude Rmn 19F, 13C et 1H De Fluoro‐1‐Hexahelicenes Et Fluoro‐1‐Heptahelicenes

1‐Fluorohexahelicene, 1‐fluoroheptahelicene and 12 substituted derivatives of these fluorohelicenes have been synthesized by the photocyclodehydrogenation of 1‐fluoro‐11‐styrylbenzo[c]phenanthrenes (Table 2) and 1‐fluoro‐13‐styrylpentahelicenes (Table 4) respectively. The photocyclisations to heptahelicenes were accompanied in five cases, by a side reaction, namely a protodefluoration. A new synthesis of heptahelicene is described (25±18: 40%). 1H, 19F and 13C‐NMR spectra are discussed. 19F and 13C‐NMR spectra of 1‐fluoro‐, 1‐fluoro‐13‐methyl‐ and 1‐fluoro‐13‐methoxycarbonylpentahelicene (8d, 8a and 8 R=‐CO2CH3) are also included. Copyright © 1985 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim