Nickel-Catalyzed Construction of Chiral 1-[6]Helicenols and Application in the Synthesis of [6]Helicene-Based Phosphinite Ligands
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.