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RESEARCH PRODUCT

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

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description

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)