Chiral Binaphthyldimethyl η ⁶ -Benzene Ligands: Design, Synthesis, and Application in Ruthenium-Catalyzed Asymmetric C–H Activation

Asymmetric catalysis enabled by a chiral η 6 -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 η 6 -benzene binding sites, hence enabling the successful preparation of the targeted chiral BenRu II catalysts. Significantly outperforming our earlier chiral BenRu II 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).