Chiral Binaphthyldimethyl η6-Benzene Ligands: Design, Synthesis, and Application in Ruthenium-Catalyzed Asymmetric C-H Activation.

Asymmetric catalysis enabled by a chiral η6-benzene (Ben) metal catalyst is an emerging field with the core challenge lying in the development of effective chiral Ben ligands. This work reports the design and synthesis of a novel class of chiral Ben ligands, namely, binaphthyldimethyl Ben ligands. In this case, a chiral binaphthyl scaffold is linked via a methylene spacer to a benzene ring that serves as the metal-coordination site. Crucially, the Ben ligands coordinate to ruthenium (Ru) in a site-specific manner despite possessing multiple potential η6-benzene binding sites, hence enabling the successful preparation of the targeted chiral BenRuII catalysts. Significantly outperforming our earlier chiral BenRuII catalysts, the system reported herein enables highly efficient phenol-directed asymmetric C-H activation of 1-aryl-2-naphthols with alkynes, providing facile access to diverse chiral spirocyclic compounds featuring an all-carbon quaternary stereocenter in high yields (up to 99%) and with excellent enantioselectivity (up to 97% ee).