Synthesis of Indoline‐Fused 2,5‐Diketopiperazine Scaffolds via Ugi‐4CR in the Basic Mediated Tandem Consecutive Cyclization

This study has developed a method to prepare diastereo‐ and regio‐selective indoline‐fused 2,5‐diketopiperazine scaffolds. The synthetic process involved an Ugi four‐component reaction in which readily available starting materials were used and a metal‐free intramolecular post‐Ugi tandem consecutive 5‐exo‐trig/6‐exo‐dig cyclization under basic conditions. The plausible mechanism and substrate structures were elucidated by single‐crystal X‐ray diffraction analysis and supported by density functional theory calculations.