A Readily Accessible Class of Chiral Cp Ligands and their Application in Ru-II-Catalyzed Enantioselective Syntheses of Dihydrobenzoindoles

Chiral cyclopentadienyl (Cp-x) ligands have a large application potential in enantioselective transition-metal catalysis. However, the development of concise and practical routes to such ligands remains in its infancy. We present a convenient and efficient two-step synthesis of a novel class of chiral Cp-x ligands with tunable steric properties that can be readily used for complexation, giving (CpRhI)-Rh-x, (CpIrI)-Ir-x, and (CpRuII)-Ru-x complexes. The potential of this ligand class is demonstrated with the latter in the enantioselective cyclization of azabenzonorbornadienes with alkynes, affording dihydrobenzoindoles in up to 98:2 e.r., significantly outperforming existing binaphthyl-derived Cp-x ligands.