A ring forming reaction or ring-closing reaction in organic chemistry is an umbrella term for a variety of reactions that introduce one or more rings into a molecule.
A heterocycle forming reaction is a reaction that introduces a new heterocycle.
[1][2] Important classes of ring forming reactions include annulations[3] and cycloadditions.
Heterocyclic compounds are useful in spectroscopic identification of compounds, purity criteria, and investigating the molecular electronic structures.
[4] Named ring forming reactions include (not exhaustive):