pyrrolidines

Pyrrolidines are a class of heterocyclic amines consisting of a five-membered ring in which four carbon atoms and one nitrogen atom form a saturated ring. The parent compound, pyrrolidine, has the formula C4H9N. The ring is the saturated analog of the aromatic pyrrole, and the nitrogen is a secondary amine. Substitutions at nitrogen (N-substituted pyrrolidines) and at carbon positions give a broad family of compounds, including 2-, 3-, 4-, and 5-substituted pyrrolidines.

Properties: The ring is flexible; the nitrogen is basic and can be protonated to give pyrrolidinium salts. These compounds are typically colourless solids or liquids and show typical amine reactivity, such as alkylation, acylation, and formation of amide derivatives. N-alkyl and N-aryl pyrrolidines are common in organic synthesis and medicinal chemistry.

Occurrence and synthesis: Pyrrolidines occur in nature (for example as motifs in alkaloids) and as important synthetic building blocks. They can be prepared by various routes, including cyclization of 4-aminobutanal derivatives, intramolecular condensation of amino alcohols, or hydrogenation of pyrroles. The ring can be stereochemically rich, leading to chiral pyrrolidines used as enantioenriched building blocks.

Applications: Pyrrolidine rings are found in many pharmaceuticals and agrochemicals. The parent proline and its derivatives are common amino acid motifs; nicotine contains a pyrrolidine ring. N-substituted pyrrolidines are used as scaffolds in medicinal chemistry and as ligands for asymmetric catalysis. The chemistry of pyrrolidines emphasizes functionalization at nitrogen and at ring carbons to access diverse libraries.