Synthesis of Stable Betaines Based on 1H-Pyrrole-2,3-diones and Pyridinium Ylides and Their Thermal Conversion to Cyclopropane-Fused Pyrroles

Pyridinium ylides, along with related azaheterocyclic ylides, are widely used in synthetic organic chemistry. However, reactions that yield stable zwitterionic adducts from these ylides remain underexplored. In this work, we demonstrate that the reaction of pyrrole-2,3-diones with in situ-generated pyridine-based azomethine ylides affords stable zwitterionic adducts, which are typically transient species in analogous processes. These betaines are used as key intermediates for the synthesis of cyclopropane-fused pyrroles or pyridine-2,3-diones via thermolysis in chlorobenzene.