Pyrrolidine, also known as tetrahydropyrrole, is a saturated five-membered heterocyclic ring, which is miscible with water. Pyrrolidine exists in many alkaloids and drug molecules, such as kappa opioids, antagonists of dopamine D4 receptors, and HIV reverse transcriptase inhibitors.
Tetrahydrofuran is a heterocyclic organic compound with the molecular formula C4H8O. Tetrahydrofuran belongs to ethers and is the complete hydrogenation product of furan. It is a colorless, water-miscible organic liquid with small viscosity at normal temperature and pressure. Because of its long liquid range, it is a commonly used medium polar aprotic solvent. Its main use is as a precursor of high molecular polymers.
When the ends of the chains are joined together into a ring, cyclic compounds result; such substances often are referred to as carbocyclic or alicyclic compounds. Substitution of one or more of the ring carbon atoms in the molecules of a carbocyclic compound with a heteroatom gives a heterocyclic compound.