Five-Membered Heterocycles Furan, Pyrrole, and Thiophene

Five-Membered Heterocycles Furan, Pyrrole, and Thiophene 

Now let us examine rather different types of heteroaromatic compounds those with five-membered rings. Furan, pyrrole, and thiophene are important five-membered ring heterocycles with one heteroatom. 

Numbering begins with the heteroatom and proceeds around the ring. 

The most important commercial source of furans is furfural (2-furaldehyde), obtained by heating oat hulls, corn cobs, or straw with strong acid. These naturally occurring materials are polymers of a five-carbon sugar, which is dehydrated by the acid to furfural. 

Pyrrole is obtained commercially by distillation of coal tar or from furan, ammonia, and a catalyst. Thiophene is obtained by heating a mixture of butanes and butenes with sulfur. 

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