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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.
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) .
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:
Primary amines are usually not used for enamine synthesis due to the preferential formation of the more thermodynamically stable imine species. [11] 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).
The Trofimov reaction is a powerful reaction for building pyrroles in total synthesis. The starting ketoxime can be prepared simply by condensing hydroxylamine on a ketone. Starting from a ketone allows for a wide range of starting materials as ketones are one of the most common functional groups in organic chemistry.
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.
Pyrrolidine is a base. Its basicity is typical of other dialkyl amines. [7] Relative to many secondary amines, pyrrolidine is distinctive because of its compactness, a consequence of its cyclic structure. Pyrrolidine is used as a building block in the synthesis of more complex organic compounds.
Amine. In chemistry, amines (/ ə ˈ m iː n, ˈ æ m iː n /, [1] [2] UK also / ˈ eɪ m iː n / [3]) are compounds and functional groups that contain a basic nitrogen atom with a lone pair.Formally, amines are derivatives of ammonia (NH 3 (in which the bond angle between the nitrogen and hydrogen is 107°), wherein one or more hydrogen atoms have been replaced by a substituent such as an ...