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

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.

Automated summary

An effective method for synthesizing 2-substituted indoles through addition/reductive cyclization in a one-pot tandem reaction has been presented. This method tolerates a wide range of functional groups and provides moderate to good yields. The gram-scale synthesis of 2-substituted indole has also been demonstrated. This protocol offers an alternative route for the synthesis of 2-substituted indoles.