Mechanochemistry‐Driven Borrowing Hydrogen Processes for Ru‐Catalyzed <i>N</i> ‐Alkylation: A Pathway to Enhanced Sustainability and Efficiency

Abstract This study presents the first mechanochemical borrowing hydrogenation (BH) strategy, offering a direct and efficient route to N ‐alkylated amines and heterocycles. This solvent‐free approach overcomes many challenges associated with conventional solution‐based syntheses, such as toxic reagents, inert atmospheres, high temperatures, lengthy reaction times, excessive catalyst loadings, and the use of solvents. By applying this method under mechanochemical conditions and employing a readily available ruthenium‐based catalyst, we achieved high conversions of a diverse set of primary amines and alcohols into N ‐alkylated amines. Furthermore, kinetic isotope effect ( KIE ) studies and Hammett analyses provided key insights into the underlying reaction mechanism. Ultimately, this protocol expands synthetic possibilities by facilitating the preparation of heterocycles.