Zirconium-catalysed N-acylation of lactams using unactivated carboxylic acids

A large number of chemicals including surfactants, nootropic drugs and pesticides contain an N-acylated lactam moiety in their molecular structure. In this work, the direct, catalytic N-acylation of a number of lactams with various unactivated carboxylic acids is reported. Several Lewis acid catalysts were evaluated for their activity in the N-acylation of pyroglutamic acid methyl ester with palmitic acid; the highest activities were observed for zirconium-based catalysts. Yields of up to 97% were obtained utilising 10?mol% Zr(propoxide)₄ in mesitylene at reflux temperature, but ZrOCl₂·8H₂O was determined as the most stable catalyst. The substrate scope was investigated and a number of lactam-carboxylic acid combinations were successfully converted into the desired products in 57–97% yield. This method provides an alternative synthetic pathway towards the drug aniracetam, which can be produced in 84% yield. A plausible catalytic mechanism is presented based on kinetic experiments.