3-(Dimethylamino)-2,2-dimethyl-2H-azirine (1) reacts with carboxylic acids at 0-25° to give 2-acylamino-N,N,2-trimethylpropionamides (= 2-acylamino-N,N-dimethylisobutyramide, acyl-Aib-NMe2) in excellent yields (Scheme 2 and 3). Examples of alpha-amino-, alpha-hydroxy-, and alpha-mercapto-carboxylic acids are given. On treatment with HCI in toluene, the terminal dimethylamide group is selectively converted to the corresponding carboxylic acid (acyl-Aib) via an amide cleavage (Scheme 4 and 5); 1,3-oxazol-5(4H)-ones are intermediates of this amide hydrolysis. This reaction sequence has been used for the extension of peptide chains (Scheme 6). The synthesis of Aib-oligopeptides using this methodology is described (Scheme 8).