cyclotrimerize

Cyclotrimerization refers to a chemical reaction in which three molecules combine to form a cyclic product. In organic chemistry the best-known example is the cyclotrimerization of alkynes, in which three alkyne units couple to give a 1,3,5-triarylbenzene core. The reaction is commonly catalyzed by transition-metal complexes such as cobalt, nickel, iron, molybdenum, or ruthenium catalysts. Conditions range from elevated temperatures to, in some cases, pressure, and may employ ligands or co-catalysts that facilitate metal-mediated assembly of the three alkyne moieties. Mechanistic proposals involve the formation of metallacyclic intermediates that reorganize to aromatize into the benzene ring.

Substrate scope includes terminal and internal alkynes, with substituents (aryl or alkyl groups) that influence reactivity and regioselectivity. Often three identical alkynes yield a symmetrical 1,3,5-triarylbenzene, while mixed alkynes can give substituted benzenes or mixtures depending on reaction conditions.

Applications of cyclotrimerization include the synthesis of 1,3,5-triarylbenzenes used as building blocks in organic electronics, dyes, and ligands, as well as routes to polycyclic aromatics in materials chemistry. The approach provides a convergent method to construct benzene rings from simple acyclic precursors.