Scheme 2. Potential chemical pathways of acid–base (I) and nucleophilic (II and III) catalysis (during the aminolysis of 5(4H)-oxazolones 2a and 2b by leucinamide in organic solvents) suggested as a way to account for the activity of carboxylic acids R3COOH (which include acetic acid, decanoic acid and the acylated α-amino acid Ac-d,l-Leu-OH and optically active Ac-l-Leu-OH and Ac-l-Tyr(Me)-OH).
