Hydrated ferric sulfate-catalyzed reactions of indole with aldehydes, ketones, cyclic ketones, and chromanones: Synthesis of bisindoles and trisindoles

Wayland E. Noland, Honnaiah Vijay Kumar, Grant C. Flick, Cole L. Aspros, Jong Hyeon Yoon, Andre C. Wilt, Nasim Dehkordi, Sheng Thao, Andrew K. Schneerer, Siming Gao, Kenneth J. Tritch

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

Abstract

Hydrated ferric sulfate [Fe2(SO4)3·xH2O] has been found to be an efficient catalyst for condensation of bisindoles or trisindoles with aliphatic or aryl aldehydes and ketones including methyl and ethyl-alkyl ketones, methyl aryl ketones, cyclic ketones, and 4-chromanones in 19–96% yields. Trisindoles and 2,2'-alkylidenebisindoles were obtained from indole-3-carbaldehydes or 3-methylindole in 72–84% yields. A total of 43 substrates was employed, giving 33 bisindoles, 3 trisindoles, and one 2:2 product; seventeen of these are new. The best results were obtained from heating ethanolic suspensions, with Fe2(SO4)3·xH2O loaded at 60 mg per mmol of electrophiles. The reaction times were typically 1–4 h, while hindered electrophiles required 8–24 h. These conditions were strong enough to promote 2:1 condensation of indole with substrates without forming higher-order byproducts, with few exceptions. This strategy features tolerance by the catalyst of a wide range of functional groups, readily available starting materials, simple operation, mild reaction conditions, and is environmentally friendly.

Original languageEnglish (US)
Pages (from-to)3913-3922
Number of pages10
JournalTetrahedron
Volume73
Issue number27-28
DOIs
StatePublished - 2017

Bibliographical note

Funding Information:
The authors would like to thank Professor Lawrence Que, Jr. for sharing his expertise in iron chemistry, Professor Thomas R. Hoye for use of FTIR instrumentation, and the Wayland E. Noland Research Fellowship Fund at the University of Minnesota Foundation for generous financial support of this project.

Keywords

  • Aldehyde
  • Bisindole
  • Chromanone
  • Cyclic ketone
  • Ferric sulfate
  • Trisindole

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