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. Mechanochemical ball‐milling enabled the direct amidation of esters through simple coupling under basic conditions (see scheme). A wide range of esters underwent amidation by this method with an array of primary and secondary amides without the need for a bulk solvent, catalysts, or additives.