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]