Mechanochemical Synthesis of N‐Aryl Amides from O‐Protected Hydroxamic Acids

Supramolecular intermediates in thermo-mechanochemical direct amidations

We present a solvent-free thermo-mechanochemical approach for the direct coupling of carboxylic acids and amines, which avoids activators and additives. Detailed analysis of the reactions by ex situ and in situ monitoring methods led to the observation, isolation, and characterisation of multicomponent crystalline intermediates that precede the formation of amides. We applied our methodology for the quantitative synthesis of the active pharmaceutical ingredient moclobemide.

Mechanochemical Synthesis of Primary Amides

Ball milling of aromatic, heteroaromatic, vinylic, and aliphatic esters with ethanol and calcium nitride afforded the corresponding primary amides in a transformation that was compatible with a variety of functional groups and maintained the integrity of a stereocenter α to carbonyl. This methodology was applied to α-amino esters and N-BOC dipeptide esters and also to the synthesis of rufinamide, an antiepileptic drug.

Direct Amidation of Esters by Ball Milling*

The direct mechanochemical amidation of esters by ball milling is described. The operationally simple procedure requires an ester, an amine, and substoichiometric KOtBu and was used to prepare a large and diverse library of 78 amide structures with modest to excellent efficiency. Heteroaromatic and heterocyclic components are specifically shown to be amenable to this mechanochemical protocol. This direct synthesis platform has been applied to the synthesis of active pharmaceutical ingredients (APIs) and agrochemicals as well as the gram-scale synthesis of an active pharmaceutical, all in the absence of a reaction solvent.