Ball-milling-driven piezoelectric-additive-free Sandmeyer reaction

The Sandmeyer reaction, a cornerstone transformation in organic synthesis, has been extensively employed for the preparation of aryl halides in both academic and industrial contexts. Nevertheless, the stoichiometric copper reagents and strongly oxidizing acidic conditions have posed significant limitations, resulting in environmental and economic challenges. In alignment with green chemistry principles, we herein report the first piezoelectric-additive-free mechanochemical protocol for Sandmeyer-type halogenation (I, Br, Cl), which provides a sustainable and efficient strategy for aryl halide synthesis. This method operates under mild conditions, featuring short reaction times, solvent-less processes, and the absence of exogenous metals or piezoelectric materials, making it both eco-friendly and cost-effective. Additionally, a radical relay halogenation to access C(sp³) halides was explored, achieving acceptable yields using styrene or [1.1.1]propellane as radical acceptors. The versatility and efficiency of this mechanochemical approach position it as a promising tool for broader applications in synthetic chemistry.