The Mechanochemical Beckmann Rearrangement: An Eco-efficient “Cut-and-Paste” Strategy to Design the “Good Old Amide Bond”

Discovered over a century ago, Beckmann rearrangement is still today fully compliant with all the green chemistry principles and consistent with the key aspects of sustainable development. Herein, we report on a sustainable mechanochemical procedure allowing the design of new amide frameworks via an eco-efficient "cut-and-paste" process of C–C and C–N bonds on the oxime backbone. We combined inexpensive and readily available reagents, such as p-tosyl imidazole (p-Ts-Im) and oxalic acid, to prepare smoothly and in good to high yields a library of structurally different amides, including value-added marketed compounds such as ε-caprolactam and the active pharmaceutical ingredient (API) paracetamol. This solvent-free mechanochemical procedure has also been optimized and successfully extended to several ketones serving as oxime precursors.