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Synthesis, Reactions and Medicinal Uses of Pyrrole

By passing furan over ammonia, steam, and pyrrole catalysts like SiO2 and Al2O3, pyrrole can be derived from furan industrially.

Pyrrole

Synthesis

By passing furan over ammonia, steam, and pyrrole catalysts like SiO2 and Al2O3, pyrrole can be derived from furan industrially.


Hantzsch pyrrole synthesis - Pyrole occurs when ammonia/primary amine is reacted with a β -haloketone or aldehyde and a β-ketoester or β-chloromethane. In addition to its role as a catalyst, the base is a reactant.


Knorr pyrrole synthesis - A widely used method is to condensate α- amino ketone with a dicarbonyl compound containing an electron-withdrawing group α, resulting in an activated methylene group (i.e., carbonyl).


Paal-Knorr pyrrole synthesis - A substituted pyrrole is formed by condensing 1,4-dicarbonyl compounds with ammonia or a primary amine. Sucinaldehyde and ammonia are used to create pyrrole.


Barton-Zard synthesis - Pyrole is the product of adding isocyanoacetate to nitroalkene, followed by cyclization and removal of the group.


From the distillation of succinimide -
Succinimide is distilled with zinc dust to produce pyrrole.


From acetylene and ammonia - Pyrole is made by diluting acetylene and ammonia using a red hot tube.



Reactions

There is no such thing as a π - excessive ring in pyrrole, furan, or thiophene. Due to this, all of these rings are susceptible to electrophilic substitution reactions at the carbons of the rings. According to the reactivity order for electrophilic attacks, pyrrole > furan > thiophene > benzene. Pyrrole's greater reactivity towards electrophiles derives from the N atom's greater ability to release electrons compared to oxygen and sulfur atoms. The most reactive compound is thiophene.

Heterocycles are characterized by β - excessive rings. All nucleophilic substitution reactions of these heterocycles except deprotonation at the C-atom or N-atom have less reactivity. Pyrrole is an inactive weak base and an inactive weak acid. For example,


Protons attached to nitrogen atoms are easily deprotonated by both acid and alkali. Deprotonation of carbon atoms only occurs under acidic conditions.

Alkylation and arylation - If an alkyl halide are dissolved in sodium or potassium salt, it forms an N-alkylpyrrole. A pyrrole ring with electron-withdrawing substituents is more likely to undergo N-alkylation and N-arylation.


A mono-C-alkylation of pyrrole cannot be achieved by direct reaction with alkyl halides

Acylation - The reaction between pyrrole and acetic anhydride produces 2-acetylpyrrole at 200°C, while the reaction between pyrrole and N-acetyl imidazole yields N-acetylpyrrole.



Reimer-Tiemann reaction - If pyrrole is combined with a strong base and chloroform, a Reimer-Tiemann reaction occurs.



Ring expansion - Heat and sodium ethoxide expand pyrrole into pyridine (six-membered ring).


Vilsmeier-Haack reaction - To formylate pyrrole, phosphorus oxychloride and dimethylformamide are used. 2 - Pyrrole carbaldehyde is produced by hydrolyzing the intermediate by a mild base.



Oxidation and reduction - Upon oxidation, Pyrrole is converted into maleimide, which on reduction is converted into Pyrolidine.



Medicinal Uses

By oxidizing Pyrrole, it becomes maleimide, and by reducing it, it becomes Pyrolidine. In addition to tolmetin, ketorolac, and sunitinib, elopiprazole, procyclidine, and atorvastatin include pyrrole rings. Ketorolac, sunitinib, age life in, and procyclidine contain pyrrole rings.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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