Hélicènes pontés: Ethano‐3,15‐ et oxa‐2‐propano‐3,15‐[7]hélicène. Synthèse, spectrographie 1H‐RMN. et étude par diffraction aux rayons X

Bridged helicenes: 3,15‐ethano‐ and 3,15‐(2‐oxapropano)‐[7]helicene The title compounds (35 and 33, see Scheme 4) have been synthesized from a common intermediate: 3,15‐dimethoxycarbonyl‐[7]helicene (26). The conformation of the bridged [7]helicenes (X‐ray diffraction) and their 1H‐NMR. spectra have been compared to the conformation and 1H‐NMR. spectra of [7]helicene and 3,15‐dimethyl‐[7]helicene (10).