Electro‐Mechanochemical Atom Transfer Radical Cyclizations using Piezoelectric BaTiO3

The formation and regeneration of active CuI species is a fundamental mechanistic step in copper‐catalyzed atom transfer radical cyclizations (ATRC). Typically, the presence of the catalytically active CuI species in the reaction mixture is secured by using high CuI catalyst loadings or the addition of complementary reducing agents. In this study it is demonstrated how the piezoelectric properties of barium titanate (BaTiO3) can be harnessed by mechanical ball milling to induce electrical polarization in the strained piezomaterial. This strategy enables the conversion of mechanical energy into electrical energy, leading to the reduction of a CuII precatalyst into the active CuI species in copper‐catalyzed mechanochemical solvent‐free ATRC reactions. Squeezing electrons by milling: Macroscopic mechanical forces transduced by ball milling are capable of inducing electrical polarization in piezoelectric BaTiO3. The electropotential of the strained piezoelectric material was harvested to trigger the reduction of a CuII complex into an active CuI catalyst for mechanochemical solvent‐free ATRC reactions.