Cyclizes

Cyclizes is the verb form of cyclize, meaning to form a ring. In chemistry, cyclization refers to a reaction or process that converts a linear or branched precursor into a cyclic compound, typically via an intramolecular bond-forming step. The term is commonly used to describe the final step in the synthesis of a cyclic product or a biosynthetic event in which a linear precursor is transformed into a ring.

Mechanisms and types: Cyclization can proceed through various pathways, including cycloadditions, radical cyclizations, cationic or anionic closures, and ring-closing metathesis. The outcome is a ring of specific size; ring sizes of five or six atoms are especially favorable due to relatively low strain and favorable kinematics. Cyclization can be disfavored by entropic costs for bringing ends together, competing intermolecular reactions, or the need to form less stable rings.

Applications: Cyclization is a common strategy in organic synthesis and natural product biosynthesis for building cyclic structures such as lactones, lactams, and carbocycles. Examples include intramolecular aldol or Claisen-type condensations, Dieckmann cyclizations, lactamization, and ring-closing metathesis. Enzymatic cyclizations in terpene and polyketide pathways produce complex cyclic architectures.

Practical considerations: Reactions are often performed under conditions that minimize intermolecular polymerization, such as dilute solutions, templating strategies, or catalytic systems. The choice of catalyst, solvent, and temperature influences ring size, stereochemistry, and yield.

See also: cyclization reaction; ring-closure; ring-closing metathesis; biosynthesis.