Sequential functionalization of pyrazole 1-oxides via regioselective metalation: synthesis of 3,4,5-trisubstituted 1-hydroxypyrazoles

J Org Chem. 2002 May 31;67(11):3904-7. doi: 10.1021/jo015997i.

Abstract

A range of 3,5-diarylated and 3,4,5-triarylated 2-(4-methoxybenzyl)pyrazole 1-oxides have been prepared by regioselective deprotonation at C-5 or bromine-magnesium exchange at C-3 or C-4 followed by transmetalation with ZnCl(2) and palladium(0)-catalyzed cross-coupling. Furthermore, the metalated pyrazole 1-oxides could be trapped with electrophiles. The sequential metalation/functionalization of the pyrazole 1-oxides may follow the order C-5, C-3, C-4, or alternatively the order C-3, C-5, C-4. The 4-methoxybenzyl group of the functionalized 2-(4-methoxybenzyl)pyrazole 1-oxides could be removed by treatment with TFA and i-Pr(3)SiH in CH(2)Cl(2), providing the corresponding functionalized 1-hydroxypyrazoles.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Magnesium / chemistry
  • Metals / chemistry*
  • Oxides / chemical synthesis*
  • Palladium / chemistry
  • Pyrazoles / chemical synthesis*
  • Substrate Specificity
  • Zinc / chemistry

Substances

  • Metals
  • Oxides
  • Pyrazoles
  • Palladium
  • Magnesium
  • Zinc