Synthesis of indole derivatives from the S₃^•−-mediated intramolecular cyclization of o-alkynylanilines

Abstract

A new method for the synthesis of 2-(phenyl)indole via the cyclization of 2-(phenylethynyl)aniline in the presence of K₂S was established, which was used to prepare 2-(phenyl)indole derivatives in high yields (66%-93%). Mechanistic studies have revealed that a trisulfur radical anion (S₃^•−) is generated from K₂S, which acts as an initiator for the intramolecular addition of the alkyne and the amino group in o-alkynylaniline, ultimately leading to the formation of the indole derivative. This method provides a new way to prepare 2-(phenyl)indoles and a novel application of S₃^•− in organic synthesis.

Graphical Abstract

Keyword:

• 2-(phenyl)indoles
• K₂S
• o-alkynoanilines
• trisulfur radical anion

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Funding

We thank Natural Science Foundation of Inner Mongolia Autonomous Region (2021ZD02 and 2021MS02021), Program for Grassland Excellent Talents of Inner Mongolia Autonomous Region, Foundamental Research Funds for Inner Mongolia Universities (JY20220125) and Innovative Research Team in Universities of Inner Mongolia Autonomous Region (NMGIRT2212) for financial support.