π-Extended Redox-Active Ligand-Promoted Cobalt-Catalyzed Diastereo- and Enantioselective Borylcyclopropanation of Alkenes.

Chiral cis-cyclopropylboronates are valuable platform intermediates for the modular synthesis of structurally diverse cis-cyclopropane derivatives, but direct catalytic access to them from simple alkenes has not been achieved. Here, we report a practical and scalable cobalt-catalyzed enantioselective borylcyclopropanation using commercially available starting materials, delivering enantioenriched cis-cyclopropylboronates as programmable platform intermediates, typically in >99% ee and >20/1 dr. The C-B bond provides a stereoretentive handle for downstream transformations, enabling stereospecific access to a broad range of functionalized cis-cyclopropanes (CCPs), including valuable cis-cyclopropylamines and medicinally relevant scaffolds, without erosion of stereochemical integrity. Mechanistic studies support a polarized Co-carbene/alkene [2 + 2] cycloaddition manifold in which a π-extended redox-active ligand modulates the electronic structure of the Co-carbene and biases alkene orientation to deliver the cis enantiomer selectively. This work delivers a practical route from simple starting materials to stereodefined, easy-to-modify scaffolds, enabling broader use of chiral CCPs in drug discovery.