NBS-Promoted Synthesis of Maleimides by Oxidative Dearomatization of Pyrroles: Mechanistic Investigations Using Online MS in Real-Time

Oxidative dearomatization of pyrroles is an important organic transformation to deliver pharmaceutically important compounds, especially the synthesis of diaryl maleimides via the dearomatization of pyrroles has always been challenging. Herein, we report an unprecedented protocol for synthesizing functionalized maleimides by NBS-promoted oxidative dearomatization of 2,3,4-trisubstituted pyrroles. The reaction proceeds via three sequential reactions: dearomatization, oxidation, and detosylation. The use of online EI mass spectrometry has enabled the mechanistic analysis of the reaction by capturing several short-lived intermediates and monitoring the progress of the reaction in real-time.