Iridium- and ruthenium-catalysed synthesis of 2,3-disubstituted indoles from anilines and vicinal diols

Org Biomol Chem. 2010 Dec 21;8(24):5576-82. doi: 10.1039/c0ob00106f. Epub 2010 Oct 20.

Abstract

A straightforward and atom-economical method is described for the synthesis of 2,3-disubstituted indoles. Anilines and 1,2-diols are condensed under neat conditions with catalytic amounts of either [Cp*IrCl(2)](2)/MsOH or RuCl(3)·xH(2)O/phosphine (phosphine = PPh(3) or xantphos). The reaction does not require any stoichiometric additives and only produces water and dihydrogen as byproducts. Anilines containing methyl, methoxy, chloro and fluoro substituents can participate in the cyclocondensation. Meta-substituted anilines give good regioselectivity for 6-substituted indoles, while unsymmetrical diols afford excellent regioselectivity for the indole isomer with an aryl or large alkyl group in the 2-position. The mechanism for the cyclocondensation presumably involves initial formation of the α-hydroxyketone from the diol. The ketone subsequently reacts with aniline to generate the α-hydroxyimine which rearranges to the corresponding α-aminoketone. Acid- or metal-catalysed electrophilic ring-closure with the release of water then furnishes the indole product.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alcohols / chemistry*
  • Aniline Compounds / chemistry*
  • Catalysis
  • Indoles / chemical synthesis*
  • Iridium / chemistry*
  • Molecular Structure
  • Ruthenium / chemistry*

Substances

  • Alcohols
  • Aniline Compounds
  • Indoles
  • Iridium
  • Ruthenium
  • aniline