NaI‐promoted Synthesis of Dihydroquinolines via an Unusual Azetine Intermediate

Abstract

New approaches to improve Skraup‐type reactions for large‐scale synthesis of 1,2‐dihydroquinolines (1,2‐DHQs) are highly desirable yet challenging in synthetic chemistry. Herein, an efficient sodium iodide‐promoted Skraup‐type reaction of anilines with ketones has been developed at low loading of HBF4 (0.5 mol%), thus providing a sustainable and economical strategy for the synthesis of 1,2‐DHQs. A variety of 1,2‐DHQs were obtained in moderate to good isolated yields. The practicality of this strategy was well demonstrated by a hundred‐gram‐scale synthesis of 6‐fluoro‐2,2,4‐trimethyl‐1,2‐dihydroquinoline in 68% isolated yield. Intriguingly, an unusual azetine intermediate was successfully isolated and structurally determined by NMR and MS, indicating of an unprecedented mechanism for Skraup‐type quinoline synthesis.