Regioselective 1,2-Alkylboration of Benzylidenecyclopropanes: Access to Csp³-Enriched Cyclopropyl Boronic Esters

We describe a novel, regioselective alkylboration of versatile (hetero)benzylidenecyclopropanes with beta-H-containing alkyl iodides and bis(pinacolato)diboron enabled by copper catalysis. This three-component method allows for consecutive B-Csp(3) and Csp(3)-Csp(3) bond formation to access Csp(3)-enriched diverse tertiary cyclopropyl boronic esters with broad functionality tolerance, and the so-formed C-B bond is amenable to further structural diversification. Radical clock experiment, Hammett analysis, and DFT calculation suggest a mechanism of polar, rather than radical manifold, and S(N)2-type C-C bond formation was found to be the rate-limiting step instead of migratory alkene insertion.