TBHP/TBAI-Mediated Oxidative Cascade Reaction Consisting of Dimerization, Cyclization, and 1,2-Aryl Migration: Metal-Free Synthesis of Pyrrolin-4-ones and Highly Substituted Pyrroles

Treatment of enamino esters with TBHP (t-butylhydroperoxide) and TBAI (t-butylammonium iodide) in HFIP (hexafluoroisopropanol) was found to afford a variety of substituted pyrrolin-4-one compounds. This metal-free oxidative cascade reaction consists of the key steps of coupling of two radical intermediates, an intramolecular ring closure, and an exclusive 1,2-aryl radical migration. Upon treatment with a base, the obtained pyrrolin-4-ones could be converted to the highly substituted pyrrole compounds.