The synthesis of pyrrole from a 1,4-dicarbonyl compound and ammonia is known as the Paal-Knorr synthesis. Here's the step-by-step mechanism for this reaction:1. Nucleophilic attack of ammonia on one of the carbonyl groups:The lone pair of electrons on the nitrogen atom of ammonia NH3 attacks one of the carbonyl groups C=O in the 1,4-dicarbonyl compound, forming a tetrahedral intermediate.2. Proton transfer:A proton H+ from the nitrogen atom in the tetrahedral intermediate is transferred to the oxygen atom of the adjacent carbonyl group, generating a hydroxyl group OH and an imine C=N in the molecule.3. Intramolecular cyclization:The hydroxyl group OH acts as a nucleophile and attacks the imine carbon, forming a five-membered ring with the release of a water molecule H2O .4. Tautomerization:The molecule undergoes tautomerization, where a proton H+ is transferred from the nitrogen atom to the hydroxyl group OH , resulting in the formation of a double bond C=C and a nitrogen atom with a lone pair of electrons.5. Aromatization:The molecule undergoes a final rearrangement to form the aromatic pyrrole ring. The lone pair of electrons on the nitrogen atom is delocalized into the ring, creating a conjugated system of alternating single and double bonds, which imparts aromatic stability to the pyrrole molecule.The intermediates involved in this reaction are:- Tetrahedral intermediate formed after the nucleophilic attack of ammonia - Imine and hydroxyl-containing intermediate formed after proton transfer - Five-membered ring intermediate formed after intramolecular cyclization - Tautomeric intermediate formed after tautomerization The final product is the aromatic pyrrole molecule.