Diynes metathesis

Diene, Enyne, and Diyne Metathesis in Natural Product Synthesis... 

Depending on the types of unsaturated functional units involved in the metathesis process, the reactions can be classified into three major categories diene, enyne, and diyne metathesis (Figs. 1-3). Another mode of classification... 

While diene metathesis or diyne metathesis are driven by the loss of a (volatile) alkene or alkyne by-product, enyne metathesis (Fig. 2) cannot benefit from this contributing feature to the AS term of the reaction, since the event is entirely atom economic. Instead, the reaction is driven by the formation of conjugated dienes, which ensures that once these dienes have been formed, the process is no longer a reversible one. Enyne metathesis can also be considered as an alkylidene migration reaction, because the alkylidene unit migrates from the alkene part to one of the alkyne carbons. The mechanism of enyne metathesis is not well described, as two possible complexation sites (alkene or alkyne) exist for the ruthenium carbene, leading to different reaction pathways, and the situation is further complicated when the reaction is conducted under an atmosphere of ethylene. Despite its enormous potential to form mul-... 

Fig. 3a,b Typical diyne metathesis reactions ring-closing alkyne metathesis (RCAM, a) diyne cross metathesis (ACM, b)... 

Fig. 5 Diyne metathesis initiators used in Fiirstner s natural product syntheses...

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