Synthesis of 13–16‐Membered Cyclotetrapeptide Mimics by Ugi Reactions with Diacids and Diisonitriles

13–16‐Membered cyclic tetraamides were synthesized by Ugi reactions using diisonitriles and dicarboxylic acids in 2,2,2‐trifluoroethanol without (pseudo) high dilution conditions. Structures of these cyclic tetraamides were investigated by NMR and X‐ray crystallography. Chemical libraries of 13–16‐membered cyclic tetraamides were conveniently and quickly synthesized by multi‐component Ugi reactions. The conformations of some cyclic tetraamides were studied by X‐ray crystallography and NMR experiments.