Elucidation of a Side Reaction During Acylation of Primary Amines with Fatty Acid Chlorides

In the presence of a tertiary base the well‐known acylation of primary amines with fatty acid chlorides yields 4‐alkylidene‐3‐alkyloxetanones 10 as byproducts, which can acylate the amino compound to give the α‐alkyl‐β‐keto amide 11. This so far not observed side reaction has been detected for the first time during the acylation of L‐cystine di‐tert‐butyl ester with palmitoyl chloride, however, analoguous side products may be obtained with any other amino acid ester or amino compound in general.