New Ugi/Pictet-Spengler Multicomponent Formation of Polycyclic Diketopiperazines from Isocyanides and α-Keto Acids

A new four-component 1,4-diketopiperazine formation is described via an Ugi/Pictet-Spengler two-step procedure. The use of α-ketocarboxylic acids and homoveratryl isocyanide allows the formation of α-keto amides along with cyclised 6-hydroxy­piperazines. The mixtures are not separated but directly treated with trifluoroactic acid to afford a tricyclic 2,5-diketopiperazine in a ­Pictet-Spengler-type cyclisation.