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)