Site-selective electrophilic cyclization and subsequent ring-opening: a synthetic route to pyrrolo[1,2-a]quinolines and indolizines

J Org Chem. 2012 Oct 5;77(19):8562-73. doi: 10.1021/jo3015374. Epub 2012 Sep 17.

Abstract

An efficient strategy for the synthesis of pyrrolo[1,2-a]quinolines and indolizines from pyranoquinolines via site-selective electrophilic cyclization and subsequent opening of pyran ring using silver/iodine under mild reaction conditions is described. This approach involves the preferential attack of the pyridyl nitrogen over aryl ring and leads to the formation of 5-endo-dig cyclized products. Quantum chemical calculations between C-N (ΔE(a) = 9.01 kcal/mol) and C-C (ΔE(a) = 31.31 kcal/mol) bond formation were performed in order to rationalize the observed site selectivity. Structure of the products were confirmed by the X-ray crystallographic studies. Iodo-substituted compounds generated by the electrophilic iodocyclization were further diversified via Pd-catalyzed cross-coupling reactions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Catalysis
  • Cross-Linking Reagents / chemistry*
  • Crystallography, X-Ray
  • Cyclization
  • Indolizines / chemical synthesis*
  • Molecular Structure
  • Palladium / chemistry*
  • Pyrroles / chemical synthesis*
  • Pyrroles / chemistry
  • Quantum Theory
  • Quinolines / chemical synthesis*
  • Quinolines / chemistry
  • Stereoisomerism

Substances

  • Cross-Linking Reagents
  • Indolizines
  • Pyrroles
  • Quinolines
  • Palladium