Ring-Chain Tautomerism. I: Synthetic Applications of Heterocycles with One Heteroatom (A Review)

The intermolecular arrangements leading to isomerization due to ring opening or cyclization is known as ring−chain tautomerism. The formation of some important heterocyclic compounds having one heteroatom via ring-chain tautomeric phenomenon is discussed. Most oxygenated or nitrogenous heterocyclic systems appeared isolated, condensed or in Spiro form. According to the size of the heterocyclic ring being formed via intramolecular addition of a heteroatom to a heteropolar multiple bond, indicated by a numerical prefix from three to six is reported in this review.