Two 1‐[6]helicenol derivatives were synthesized by Ni‐catalyzed [2+2+2] cycloaddition on a multigram scale. Both enantiomers of the 1‐[6]helicenols could be efficiently prepared by simple optical resolution. As a synthetic application of helically chiral 1‐[6]helicenols, a novel class of [6]helicene‐based phosphinites was developed; these compounds represent the first examples of helically chiral phosphinite ligands. Up to 90 % ee was obtained for the Pd‐catalyzed asymmetric allylic alkylation reaction.
The cover picture shows “Wanko Soba” (Iwate, Japan), an interesting dish of soba (buckwheat noodles). Each time that you take a mouthful of soba from a small dish, the maid refills it. The scheme illustrates the Ni‐catalyzed construction of chiral 1‐functionalized [6]helicene derivatives on a multigram scale as a result of the stepwise study for scale up. This 10 g scale synthesis of helicene derivatives by [2+2+2] cycloaddition is the largest scale in this field. The enantiomerically pure 1‐[6]helicenols can be synthesized through an efficient optical resolution process via the corresponding camphanates. Furthermore, the development of a novel class of [6]helicene‐based phosphinites and their preliminary investigation as asymmetric ligands are also described. Details are discussed in the Communication by T. Tsujihara, T. Kawano et al. on http://onlinelibrary.wiley.com/doi/10.1002/ejoc.201600677/abstract.
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