Regiodivergent Cyclizations of Donor–Acceptor Cyclopropanes with Hydrazines under Solventless, Mechanochemical Milling

We developed a regiodivergent synthesis of highly diastereoselective pyridazines and pyrazoles from DACs and hydrazines under solventless ball milling with HFIP. This HFIP-promoted mechanochemical approach eliminates the need for metal catalysts, hazardous solvents, inert atmospheres, or external heating, representing a significant advancement in sustainable heterocycle synthesis. We delineate the structural parameters that dictate the regioselectivity, providing a clear roadmap for the synthesis of either heterocyclic core. 13 C NMR studies helped to elucidate the activation of DAC by HFIP.