DBU as a Catalyst for the Synthesis of Amides via Aminolysis of Methyl Esters

Methyl benzoate and methyl p-chlorophenyl acetate react with neat benzylamine and pyrrolidine to form the corresponding amides. These reactions are faster in the presence of 20 mol% of DBU providing slight better yields. When a diester derived from L-aspartic acid was used as substrate, the reaction with benzylamine and pyrrolidine in the presence of DBU was chemoselective and led to the corresponding amides in good yields. Reaction of aspartic acid monomethyl ester with these amines led to amides having a free carboxy group (at Cl). Less nucleophilic and less basic aniline failed to form the expected products in both absence and presence of DBU. By monitoring the course of reaction by ESI-MS, key charged intermediates formed by the reactions of methyl benzoate and methyl p-chlorophenyl acetate with benzylamine were intercepted and further characterized by ESI-MS/MS.