Indium-Catalyzed Annulation of o-Acylanilines with Alkoxyheteroarenes: Synthesis of Heteroaryl[b]quinolines and Subsequent Transformation to Cryptolepine Derivatives

Molecules. 2018 Apr 5;23(4):838. doi: 10.3390/molecules23040838.


We disclose herein the first synthetic method that is capable of offering heteroaryl[b]quinolines (HA[b]Qs) with structural diversity, which include tricyclic and tetracyclic structures with (benzo)thienyl, (benzo)furanyl, and indolyl rings. The target HA[b]Q is addressed by the annulation of o-acylanilines and MeO-heteroarenes with the aid of an indium Lewis acid that effectively works to make two different types of the N-C and C-C bonds in one batch. A series of indolo[3,2-b]quinolines prepared here can be subsequently transformed to structurally unprecedented cryptolepine derivatives. Mechanistic studies showed that the N-C bond formation is followed by the C-C bond formation. The indium-catalyzed annulation reaction thus starts with the nucleophilic attack of the NH₂ group of o-acylanilines to the MeO-connected carbon atom of the heteroaryl ring in an SNAr fashion, and thereby the N-C bond is formed. The resulting intermediate then cyclizes to make the C-C bond through the nucleophilic attack of the heteroaryl-ring-based carbon atom to the carbonyl carbon atom, providing the HA[b]Q after aromatizing dehydration.

Keywords: Lewis acids; anti-cancer activity; anti-malarial activity; heteroarenes; indium; one-pot; pyridine; quindolines; tandem reaction.

MeSH terms

  • Catalysis
  • Indium / chemistry*
  • Indole Alkaloids / chemistry
  • Lewis Acids / chemistry
  • Molecular Structure
  • Quinolines / chemical synthesis*
  • Quinolines / chemistry


  • Indole Alkaloids
  • Lewis Acids
  • Quinolines
  • Indium
  • cryptolepine