Novel [6]‐ and [7]Helicene‐Like Quinones via Mono‐ and Bidirectional Chromium‐Templated Benzannulation of Bridged Binaphthyl Carbene Complexes

A new organometallic approach to novel, functionalised, helicene‐like quinones and bisquinones has been developed based on the chromium‐templated [3+2+1] benzannulation reaction. The [5]helicene‐analogous monocarbene chromium complexes 4, 5, 17 and 19, derived from dibromo‐substituted methylene‐ or silylene‐tethered binaphthols 2 and 3, react with various alkynes to give [6]helicene‐like quinones 6–13 and 20–29 after oxidative work‐up. A rare competition of angular vs. linear annulation is observed for the incorporation of phenylacetylene that affords quinones 21/22 and 28/29. Protection of the phenolic benzannulation product with camphanic acid chloride 14, followed by chromatographic separation, provides access to enantiopure [6]helicene‐like derivatives. Bidirectional benzannulation of helical biscarbene complexes 16 and 18 results in bisangular and angular‐linear bisquinones 30–36 after oxidative work‐up. X‐ray crystal structures of the heterocyclic [5]‐, [6]‐ and [7]helicene‐derivatives and the angular‐linear annulation products indicate an increasing distortion of the helical framework with progressive annulation. The CD spectra of the methylene‐tethered biaryls (3, 9, 14, 36) reflect the different interactions between the aryl chromophores; cyclovoltammetric studies of bisangular bisquinones 30 and 33 reveal three reversible, one‐electron reduction steps. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)