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Synthesis, Reactions and Medicinal Uses of Pyrazole

In the reaction between hydrazine and propargyl aldehyde, pyrazole is formed.

Pyrazole

Synthesis

In the reaction between hydrazine and propargyl aldehyde, pyrazole is formed.



In the reaction between hydrazine and propargyl aldehyde, pyrazole is formed.



By reacting diarylhydrazones with vicinal diols, 1, 3-substituted pyrazoles are formed.


Synthesis of substituted pyrazoles is caused by reaction of hydrazine salts with aldehydes/ketones that are α, β-unsaturated.


With hydrazine, a substituted pyrazole can be easily formed from a derivative of α, β-ethylene carbonyl.



Reactions

Position-1 has a nonreactive N-atom. During substitution, a proton (H atom) can easily be lost in the presence of a base. Because position-2 atoms have two electrons, they are basic and react easily with electrophiles. As a result of the combined electron richness of both N-atoms, the charge density of C3 and C5 is reduced, allowing C4 to be attacked in electrophilic fashion. In the presence of a strong base, deprotonation at C3 can occur, resulting in ring opening.



With a strong base, the N1 atom can easily lose a proton. Afterwards, an electrophile can react with the resulting nucleophile on nitrogen



Scorpionate (tridentate ligand) formation - The tridentate ligand scorpionate is formed when pyrazole reacts with potassium borohydride.



By using alkyl halides, diazomethane, or dimethylsulfate, the –NH group of pyrazole can be easily alkylated.



Position-4 is a readily available electrophilic substitution site in pyrazoles.



Oxidation reaction - A pyrazole ring may be oxidized, but the side chain may not.



Reduction reaction - Despite catalytic and chemical reductive conditions, unsubstituted pyrazole remains relatively stable. It is possible to reduce pyrazole derivatives under various conditions. For example,



Medicinal Uses

Derivatives of pyrazole are used as analgesics, antipyretics, anti-inflammatory (e.g., antipyrine, phenylbutazone, celecoxib), antibacterial, tranquilizers, anti-cancers, and diabetes medication.
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