Diastereoselective Synthesis of P-Chirogenic and Atropisomeric 2,2′-Bisphosphino-1,1′-binaphthyls Enabled by Internal Phosphine Oxide Directing Groups

Diphosphine ligands that merge both axial and P-centered chirality may exhibit superior or unique properties. Herein we report the diastereoselective introduction of P-centered chirality at the 2-position of the axially chiral 2 '-(phosphine oxide)-1,1 '-binaphthyl scaffold. A lithium-bromide exchange reaction of a 2-bromo-2 '-(phosphine oxide)-1,1 '-binaphthyl and treatment with dichlorophosphines followed by a nucleophilic organometallic reagent afforded unsymmetrical 2-phosphino-2 '-(phosphine oxide)-1,1 '-binaphthyls with binaphthyl axial chirality and one or two phosphorus stereocenters with a variety of P substituents. The final diastereomerically pure 2,2 '-bisphosphino-1,1 '-binaphthyls were obtained by reduction of the phosphine oxide directing group. Preliminary results demonstrated that a ligand with this hybrid chirality could induce higher stereoselectivity in the metal-complex-catalyzed asymmetric hydrogenation of a dialkyl ketone.