Heterocyclic chemistry is the branch of chemistry that deal with organic compounds that contain heteroatoms in addition to carbon atoms. They may be acyclic or cyclic compounds.

Heterocyclic compound is the class of cyclic organic compounds those having at least one hetero

atom (i.e. atom other than carbon) in the cyclic ring system. The most common heteroatoms are

nitrogen (N), oxygen (O) and sulphur (S). Heterocyclic compounds are frequently abundant in

plants and animal products; and they are one of the important constituent of almost one half of

the natural organic compounds known. Alkaloids, natural dyes, drugs, proteins, enzymes etc. are

some important class of natural heterocyclic compounds.