Halogen Bond‐Catalyzed Oxidative Annulation of N‐Alkyl Pyridinium Salts and Alkenes with Air as a Sole Oxidant: Metal‐free Synthesis of Indolizines

Abstract The utilization of ambient air as a sole oxidant is highly desired for the sustainability of chemical industry. Herein, we reported a mild and metal‐free synthesis of indolizines using pyridinium salts and alkenes with ambient air as a sole oxidant. In this reaction, a halogen bond donor (perfluoro‐1‐iodooctane, 10 mol%) was successfully applied to catalyze this desired oxidative [3+2] annulation. The C−I bond of halogen bond donor is crucial for this transformation, while the corresponding C−Br bond and C−F bonds gave much lower yields. Moreover, the phenolic hydroxyl increases the amount of side‐product, probably due to the strong interaction of phenolate anion and the halogen bond donor. Finally, with the rapid development of halogen bond catalysis, this halogen bond‐catalyzed strategy could continuously promote the synthesis of indolizines in a sustainable manner.