Rapid access to pyrazolo[3,4-c]pyridines via alkyne annulation: limitations of steric control in nickel-catalyzed alkyne insertions

Org Lett. 2007 Nov 22;9(24):4947-50. doi: 10.1021/ol701784w. Epub 2007 Nov 3.

Abstract

Polyfunctionalized pyrazolo[3,4-c]pyridines were readily prepared by the annulation of alkynes with tert-butyl 4-iodopyrazolocarboximines. The reaction was found to be catalyzed by both NiBr2(PPh3)2/Zn or PdCl2(PhCN)2 to yield complex heterocycles in good to moderate yields. Annulation using nickel catalysis was found to be regio-random, implying that steric control in nickel-catalyzed alkyne insertion has limitations based on the character of the Ni-C bond in the pre-insertion complex.

MeSH terms

  • Alkynes / chemistry*
  • Catalysis
  • Molecular Structure
  • Nickel / chemistry*
  • Palladium / chemistry
  • Pyrazoles / chemistry*
  • Pyridines / chemistry*
  • Stereoisomerism

Substances

  • Alkynes
  • Pyrazoles
  • Pyridines
  • Palladium
  • Nickel