Aromatic and Saturated Heterocycles
Saturated Five-Membered Heterocyclic Compounds
The ring strain of five-membered rings is relatively small. As a result, the chemical behavior of saturated five-membered heterocylic compounds resembles that of the corresponding open-chain compounds. Five-membered heterocycles are usually produced through hydrogenation of the corresponding heteroaromatic compounds that may be found in petroleum. However, on account of a number of other factors, due attention must be paid to thiophene. Since sulfur is a catalyst poison, catalytic hydrogenation may fail if an unsuitable catalyst is applied. Hydrogenation of thiophene over Raney nickel, for instance, may lead to desulfurization. Nevertheless, conversion of thiophene into tetrahydrothiophene may be successfully carried out by catalytic hydrogenation with a palladium-activated carbon catalyst.
Saturated heterocyles, such as tetrahydrofuran (THF), can often be easily synthesized by an intramolecular ring-closure substitution.
N-substituted pyrrolidine derivatives may be produced by intermolecular double substitution between 1,4-dibromobutane and the corresponding substituted amine.