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Pechmann Pyrazole Synthesis

Published Online: 15 SEP 2010

DOI: 10.1002/9780470638859.conrr484

Comprehensive Organic Name Reactions and Reagents

Comprehensive Organic Name Reactions and Reagents

How to Cite

2010. Pechmann Pyrazole Synthesis. Comprehensive Organic Name Reactions and Reagents. 484:2147–2150.

Publication History

  1. Published Online: 15 SEP 2010

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Abstract

The preparation of pyrazole derivatives involving a 1,3-dipolar cycloaddition between a diazomethane (or other diazonium salt) and a molecule with carbon-carbon double bonds to pyrazoline and subsequent oxidation is generally referred to as the Pechmann pyrazole synthesis. The study finds that carbonyl, ester, or cyano group that conjugates to the olefinic double bond, facilitates the formation of pyrazoline; whereas a phenyl group decreases the reactivity. Upon oxidation, (e.g., with bromine,) pyrazole derivatives are yielded, although the dehydrogenation some times occurs without an oxidant present. In addition, a direct preparation of pyrazole from 1,3-dipolar cycloaddition between diazomethane and acetylene has also been developed by Pechmann.

Keywords:

  • diazomethane;
  • pyrazoline;
  • p-quinones;
  • acetylene