Reversal of Regioselectivity in Asymmetric C−H Bond Annulation with Bromoalkynes under Cobalt Catalysis**

Abstract

AbstractMetal‐catalyzed asymmetric C−H bond annulation strategy offers a versatile platform, allowing the construction of complex P‐chiral molecules through atom‐ and step‐economical fashion. However, regioselective insertion of π‐coupling partner between M−C bond with high enantio‐induction remain elusive. Using commercially available Co(II) salt and chiral‐Salox ligands, we demonstrate an unusual protocol for the regio‐reversal, enantioselective C−H bond annulation of phosphinamide with bromoalkyne through desymmetrization. The reaction proceeds through ligand‐assisted enantiodetermining cyclocobaltation followed by regioselective insertion of bromoalkyne between Co−C, subsequent reductive elimination, and halogen exchange with carboxylate resulted in P‐stereogenic compounds in excellent ee (up to >99 %). The isolation of cobaltacycle involved in the catalytic cycle and the outcome of control experiments provide support for a plausible mechanism.