Cu-Catalyzed Electrochemical Atom Transfer Radical Addition with Halomalonic Esters: A Route to Cyclopropane Derivatives.

Atom transfer radical addition (ATRA) remains an important and popular synthetic method for C-C bond formation by using readily accessible alkene precursors and organic halides. We report that copper-catalyzed electrochemical ATRA (ATRA) of diethyl halomalonates (XCH(COOEt), X = Br, Cl) to a series of aromatic alkenes yields halide malonate ester intermediates that subsequently undergo facile ring closure to give cyclopropanes. The in situ spectroscopic identification of a diethyl malonatocopper(II) complex, [CuL(CH(COOEt))], serves as a key catalytic species, effectively moderating free radical concentrations during the electrochemical process to enhance product formation. Mechanistic insights into cyclopropanation were elucidated through cyclic voltammetry and UV-vis spectroelectrochemical analysis. This study presents a new mild electrochemical synthetic strategy for constructing functionalized cyclopropane derivatives.