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2.1.4.8 Conclusions

DOI: 10.1055/sos-SD-224-00028

Diesendruck, C. E.Science of Synthesis: N-Heterocyclic Carbenes in Catalytic Organic Synthesis, (2016297.

Enyne metathesis is a powerful reaction that can be used for the creation of polycyclic compounds. Furthermore, it has found many uses in the total synthesis of natural products and shape-persistent molecules. While this reaction is now considered a classical metathesis reaction, ligand optimization has not yet been performed for this specific reaction, and most advances are a consequence of improvements achieved for other metathesis reactions. Most ring-closing enyne metathesis substrates undergo reactions within a good timeframe to provide products in good yields, unless the alkyne has one (or two) large propargylic substituent(s). Cross enyne metathesis is still problematic owing to difficulties in controlling the regioselectivity and stereoselectivity, even though recent Z-selective olefin metathesis catalysts show some promise. That said, again, in these cases the catalyst was originally designed to solve an alkene metathesis challenge and was later simply used in enyne metathesis. Significant research in this reaction is still required to develop efficient enyne metathesis catalysts, in which the ligands are optimized to deal with the different reactivities of the alkenes and alkynes, and to induce selective reactions according to the catalyst and not through substrate optimization.