Cyclenynes

Cyclenynes are a class of strained cyclic hydrocarbons containing both a carbon-carbon triple bond and a ring structure. The presence of the alkyne moiety within a ring creates significant ring strain, particularly in smaller rings. The smallest possible cyclenyne is cyclooctyne, which exists as a mixture of isomers due to the geometrical constraints of forming a triple bond within an eight-membered ring. Larger cyclenynes, such as cyclononyne and cyclodecyne, exhibit less strain and are more stable.

The synthesis of cyclenynes is often challenging due to their inherent instability. Common synthetic approaches involve the elimination of halogens or other leaving groups from suitable acyclic precursors, or the manipulation of existing cyclic structures. The reactivity of cyclenynes is dominated by the strained triple bond, which can undergo various addition reactions, often with enhanced rates compared to acyclic alkynes. They are also prone to ring-opening reactions and cycloadditions.

Cyclenynes have found applications in organic synthesis, particularly in click chemistry reactions like the copper-catalyzed azide-alkyne cycloaddition (CuAAC). Their strained nature can lead to unique selectivities and reaction pathways. Research continues to explore new synthetic methods and applications for these fascinating strained molecules.