ALKYNE METATHESIS

For many enabling features & strategic qualities, contemporary alkyne metathesis is increasingly recognized as a formidable synthetic tool. Central to this development was the remarkable evolution of the catalysts during the past decades. Alkyne metathesis, which involves the exchange of alkylidyne moieties between two acetylenes, can provide a dynamic covalent route to ethynylene-linked architectures, as an alternative strategy to irreversible alkyne couplings, such as Glaser and Sonogashira couplings. The reversible alkyne metathesis process is associated with higher yields compared to irreversible coupling primarily because it circumvents over-oligomerization. The reaction generally employs a tungsten or molybdenum-based catalyst and the reaction is driven towards equilibrium by removing one of the alkyne products by vacuum, using molecular sieves or precipitation. The advent of catalysts with improved air and moisture stability has resulted in renewed interest in the use of alkyne metathesis in DCC. The main advantages over imine condensation are improved chemical stability of the alkyne linkage and rigidity of the cage framework, which can result in higher shape persistence of the final cage product.