4. Ugi's reaction

4.1 General

The Ugi reaction (also known as Ugi-4CR or U-4CR), discovered in 1959, is a four-component reaction involving an amine, an aldehyde, a carboxylic acid and an isonitrile to give α-acetamidoamide [48] [49]. Figure 24 describes the commonly accepted mechanism for this reaction. The first step is the condensation of the amine onto the aldehyde to form the corresponding imine 12, which protons in the presence of the carboxylic acid. The divalent carbon of isonitrile adds to the electrophilic iminium to give the nitrilium ion 13, which undergoes nucleophilic addition to the carboxylate ion to form the imidate 14. After an irreversible Mumm rearrangement (intramolecular acyl transfer), the...