Synthesis of Polycyclic Indoline Skeletons by Pd-Catalyzed Tandem Indole-Participated Dearomative [4 + 2] Cycloaddition Reactions

Given that polycyclic indolines are widely recognized as essential structural motifs in numerous alkaloid natural products and biologically active compounds, the development of innovative synthetic approaches for these molecules has attracted significant attention in the scientific community. Herein, we present the development of a Pd-catalyzed tandem reaction pathway, which proceeds through a Sonogashira coupling step and a propargylic Alder-ene reaction to generate the reactive indenone-allene intermediate, followed by an intramolecular indole-participated dearomative [4 + 2] cycloaddition. This method exhibits remarkable tolerance toward a variety of functional groups and facilitates the synthesis of a broad spectrum of polycyclic indolines in moderate to high yields.