For questions concerning compounds possessing rings with two or more different types of atoms.
The IUPAC Gold Book defines heterocyclic compounds as:
Cyclic compounds having as ring members atoms of at least two different elements, e.g. quinoline, 1,2-thiazole, bicyclo[3.3.1]tetrasiloxane. (DOI:10.1351/goldbook.H02798)
The term "heterocyclic" is applicable to saturated systems (e.g. pyrrolidine), partially unsaturated systems (e.g. 2*H*-pyran), and aromatic systems (e.g. pyrimidine) alike.
The Hantzsch-Widman system is used in the nomenclature of heterocyclic compounds and is outlined in the IUPAC Blue Book (Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013), section P-22.2 onwards. However, many retained names are still widely used, and indeed a number of them have been adopted as preferred IUPAC names (such as in the examples above).
There is a very large body of research on the synthesis and reactions of heterocycles, which feature heavily in natural products as well as drugs. Some examples are shown below:
- Most organic chemistry textbooks have a short introduction to heterocyclic chemistry.
- A more specialised textbook, constantly updated with references to primary literature: Joule, J. A.; Mills, K. Heterocyclic Chemistry, 5th ed.; Wiley: Chichester, U.K., 2010.
- There is a series of graduate-level lectures on heterocyclic chemistry, given by Phil Baran at TSRI, available on iTunes. The corresponding e-book developed by the group (only available on iOS) can be found here.
- Vitaku, E.; Smith, D. T.; Njardarson, J. T. Analysis of the Structural Diversity, Substitution Patterns, and Frequency of Nitrogen Heterocycles among U.S. FDA Approved Pharmaceuticals. J. Med. Chem. 2014, 57 (24), 10257–10274. DOI:10.1021/jm501100b.