Synthesis of 2‐Substituted Indoles by Pd‐Catalyzed Reductive Cyclization of 1‐Halo‐2‐nitrobenzene with Alkynes

Abstract An effective process for synthesizing 2‐substituted indoles in a one‐pot tandem reaction of 1‐halo‐2‐nitrobenzene and terminal alkynes through addition/reductive cyclization is presented. This protocol involves a Sonogashira‐type coupling reaction followed by reductive cyclization employing dppf (1,1′‐bis(diphenylphosphino)ferrocene) ligated Pd dithiolate complex as a catalyst and Zn as an inexpensive reductant. This efficient and tandem process tolerates broad functional groups with moderate to good yields. The gram‐scale synthesis of 2‐substituted indole has also been demonstrated. This protocol provides an alternative route for the synthesis of 2‐substituted indoles.