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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.
Below is one published mechanism for the reaction: [5] Mechanism for the Hantzsch Pyrrole Synthesis. The mechanism starts with the amine (1) attacking the β carbon of the β-ketoesters (2), and eventually forming an enamine (3). The enamine then attacks the carbonyl carbon of the α-haloketone (4). This is followed by the loss of H 2 O, giving ...
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). [4] The Knorr pyrrole synthesis
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.
The Chan–Lam coupling reaction, also known as the Chan–Evans–Lam coupling, is a cross-coupling reaction between an aryl boronic acid and an alcohol or an amine to form the corresponding secondary aryl amines or aryl ethers, respectively. [1] The Chan–Lam coupling is catalyzed by copper complexes. It can be conducted in air at room ...
Methyl ketone self-condensation is a side-reaction which can be avoided through the addition of TiCl 4 [12] into the reaction mixture (to act as a water scavenger). [13] [14] An example of an aldehyde reacting with a secondary amine to form an enamine via a carbinolamine intermediate is shown below: Enamine synthesis with a carbinolamine ...
This can be illustrated by the lack of a reaction with pyrrole, whereas both 1-methyl and N-benzylpyrrole derivatives are able to react. Further work by the same authors revealed that simply piperidine as the amine R group (as opposed to tetramethylpiperidine, pictured above) accelerated the rate of reaction.