Toward safer processes for C-C biaryl bond construction: catalytic direct C-H arylation and tin-free radical coupling in the synthesis of pyrazolophenanthridines

J Org Chem. 2010 Jan 15;75(2):434-41. doi: 10.1021/jo902257j.

Abstract

A series of pyrazolo[1,5-f]phenanthridine derivatives has been efficiently synthesized by a short, straightforward sequence. A tandem amine-exchange/heterocyclization of enaminones was successfully applied to the regioselective preparation of 1,5-diarylpyrazole intermediates with structure resemblance to relevant nonsteroidal anti-inflammatory drugs such as celecoxib or tepoxalin. The final key step, cyclization by intramolecular biaryl bond formation, was accomplished by two alternative methodologies: radical coupling and catalytic direct arylation via C-H activation. The scope and limitations of the two methodologies have been explored and their complementariness has been established. In addition, polymer-supported heterogeneous catalysts have been compared with homogeneous analogues. In the radical process, toxic tin derivatives have been avoided in order to employ environmentally safer protocols.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amines / chemistry*
  • Catalysis
  • Cyclization
  • Free Radicals / chemistry*
  • Heterocyclic Compounds / chemical synthesis*
  • Heterocyclic Compounds / chemistry
  • Hydrogen Bonding
  • Magnetic Resonance Spectroscopy
  • Molecular Structure
  • Phenanthridines / chemical synthesis*
  • Phenanthridines / chemistry
  • Stereoisomerism
  • Tin / chemistry*

Substances

  • Amines
  • Free Radicals
  • Heterocyclic Compounds
  • Phenanthridines
  • pyrazolo(1,5-f)phenanthridine
  • Tin