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 (eATRA) of diethyl halomalonates (XCH(COOEt)₂, 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, [Cu^IIL(CH(COOEt)₂)]⁺, 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.