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