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Pyrrole is an extremely weak base for an amine, with a conjugate acid pK a of −3.8. The most thermodynamically stable pyrrolium cation (C 4 H 6 N +) is formed by protonation at the 2 position. Substitution of pyrrole with alkyl substituents provides a more basic molecule—for example, tetramethylpyrrole has a conjugate acid pK a of +3.7.
This reaction involves the high-speed vibration milling (HSVM) of ketones with N-iodosuccinimide (NIS) and p-toluenesulfonic acid, to form an α-iodoketone in situ. This is followed by addition of a primary amine, a β-dicarbonyl compound, cerium(IV) ammonium nitrate (CAN) and silver nitrate , as shown in the scheme below:
The amine attacks the other carbonyl to form a 2,5-dihydroxytetrahydropyrrole derivative which undergoes dehydration to give the corresponding substituted pyrrole. [7] Paal–Knorr pyrrole synthesis mechanism. The reaction is typically run under protic or Lewis acidic conditions, with a primary amine.
The Knorr pyrrole synthesis is a widely used chemical reaction that synthesizes substituted pyrroles (3). [ 1 ] [ 2 ] [ 3 ] The method involves the reaction of an α- amino - ketone (1) and a compound containing an electron-withdrawing group (e.g. an ester as shown) α to a carbonyl group (2) .
The condensation reaction can be shown below: After the condensation, the pyrrole formation can proceed as normal. The Trofimov reaction can produce both N-H and N-vinyl pyrroles depending on the reaction conditions used. The N-vinyl pyrrole can be formed by the deprotonation of the pyrrole nitrogen which then attacks a second acetylene molecule.
Pyrrolines, also known under the name dihydropyrroles, are three different heterocyclic organic chemical compounds that differ in the position of the double bond.Pyrrolines are formally derived from the aromate pyrrole by hydrogenation. 1-Pyrroline is a cyclic imine, whereas 2-pyrroline and 3-pyrroline are cyclic amines.
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In coordination chemistry, the S N 1cB (conjugate base) mechanism describes the pathway by which many metal amine complexes undergo substitution, that is, ligand exchange. Typically, the reaction entails reaction of a polyamino metal halide with aqueous base to give the corresponding polyamine metal hydroxide: [ 1 ]